Age Owner Branch data TLA Line data Source code
1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * snapbuild.c
4 : : *
5 : : * Infrastructure for building historic catalog snapshots based on contents
6 : : * of the WAL, for the purpose of decoding heapam.c style values in the
7 : : * WAL.
8 : : *
9 : : * NOTES:
10 : : *
11 : : * We build snapshots which can *only* be used to read catalog contents and we
12 : : * do so by reading and interpreting the WAL stream. The aim is to build a
13 : : * snapshot that behaves the same as a freshly taken MVCC snapshot would have
14 : : * at the time the XLogRecord was generated.
15 : : *
16 : : * To build the snapshots we reuse the infrastructure built for Hot
17 : : * Standby. The in-memory snapshots we build look different than HS' because
18 : : * we have different needs. To successfully decode data from the WAL we only
19 : : * need to access catalog tables and (sys|rel|cat)cache, not the actual user
20 : : * tables since the data we decode is wholly contained in the WAL
21 : : * records. Also, our snapshots need to be different in comparison to normal
22 : : * MVCC ones because in contrast to those we cannot fully rely on the clog and
23 : : * pg_subtrans for information about committed transactions because they might
24 : : * commit in the future from the POV of the WAL entry we're currently
25 : : * decoding. This definition has the advantage that we only need to prevent
26 : : * removal of catalog rows, while normal table's rows can still be
27 : : * removed. This is achieved by using the replication slot mechanism.
28 : : *
29 : : * As the percentage of transactions modifying the catalog normally is fairly
30 : : * small in comparisons to ones only manipulating user data, we keep track of
31 : : * the committed catalog modifying ones inside [xmin, xmax) instead of keeping
32 : : * track of all running transactions like it's done in a normal snapshot. Note
33 : : * that we're generally only looking at transactions that have acquired an
34 : : * xid. That is we keep a list of transactions between snapshot->(xmin, xmax)
35 : : * that we consider committed, everything else is considered aborted/in
36 : : * progress. That also allows us not to care about subtransactions before they
37 : : * have committed which means this module, in contrast to HS, doesn't have to
38 : : * care about suboverflowed subtransactions and similar.
39 : : *
40 : : * One complexity of doing this is that to e.g. handle mixed DDL/DML
41 : : * transactions we need Snapshots that see intermediate versions of the
42 : : * catalog in a transaction. During normal operation this is achieved by using
43 : : * CommandIds/cmin/cmax. The problem with that however is that for space
44 : : * efficiency reasons, the cmin and cmax are not included in WAL records. We
45 : : * cannot read the cmin/cmax from the tuple itself, either, because it is
46 : : * reset on crash recovery. Even if we could, we could not decode combocids
47 : : * which are only tracked in the original backend's memory. To work around
48 : : * that, heapam writes an extra WAL record (XLOG_HEAP2_NEW_CID) every time a
49 : : * catalog row is modified, which includes the cmin and cmax of the
50 : : * tuple. During decoding, we insert the ctid->(cmin,cmax) mappings into the
51 : : * reorder buffer, and use them at visibility checks instead of the cmin/cmax
52 : : * on the tuple itself. Check the reorderbuffer.c's comment above
53 : : * ResolveCminCmaxDuringDecoding() for details.
54 : : *
55 : : * To facilitate all this we need our own visibility routine, as the normal
56 : : * ones are optimized for different usecases.
57 : : *
58 : : * To replace the normal catalog snapshots with decoding ones use the
59 : : * SetupHistoricSnapshot() and TeardownHistoricSnapshot() functions.
60 : : *
61 : : *
62 : : *
63 : : * The snapbuild machinery is starting up in several stages, as illustrated
64 : : * by the following graph describing the SnapBuild->state transitions:
65 : : *
66 : : * +-------------------------+
67 : : * +----| START |-------------+
68 : : * | +-------------------------+ |
69 : : * | | |
70 : : * | | |
71 : : * | running_xacts #1 |
72 : : * | | |
73 : : * | | |
74 : : * | v |
75 : : * | +-------------------------+ v
76 : : * | | BUILDING_SNAPSHOT |------------>|
77 : : * | +-------------------------+ |
78 : : * | | |
79 : : * | | |
80 : : * | running_xacts #2, xacts from #1 finished |
81 : : * | | |
82 : : * | | |
83 : : * | v |
84 : : * | +-------------------------+ v
85 : : * | | FULL_SNAPSHOT |------------>|
86 : : * | +-------------------------+ |
87 : : * | | |
88 : : * running_xacts | saved snapshot
89 : : * with zero xacts | at running_xacts's lsn
90 : : * | | |
91 : : * | running_xacts with xacts from #2 finished |
92 : : * | | |
93 : : * | v |
94 : : * | +-------------------------+ |
95 : : * +--->|SNAPBUILD_CONSISTENT |<------------+
96 : : * +-------------------------+
97 : : *
98 : : * Initially the machinery is in the START stage. When an xl_running_xacts
99 : : * record is read that is sufficiently new (above the safe xmin horizon),
100 : : * there's a state transition. If there were no running xacts when the
101 : : * xl_running_xacts record was generated, we'll directly go into CONSISTENT
102 : : * state, otherwise we'll switch to the BUILDING_SNAPSHOT state. Having a full
103 : : * snapshot means that all transactions that start henceforth can be decoded
104 : : * in their entirety, but transactions that started previously can't. In
105 : : * FULL_SNAPSHOT we'll switch into CONSISTENT once all those previously
106 : : * running transactions have committed or aborted.
107 : : *
108 : : * Only transactions that commit after CONSISTENT state has been reached will
109 : : * be replayed, even though they might have started while still in
110 : : * FULL_SNAPSHOT. That ensures that we'll reach a point where no previous
111 : : * changes has been exported, but all the following ones will be. That point
112 : : * is a convenient point to initialize replication from, which is why we
113 : : * export a snapshot at that point, which *can* be used to read normal data.
114 : : *
115 : : * Copyright (c) 2012-2026, PostgreSQL Global Development Group
116 : : *
117 : : * IDENTIFICATION
118 : : * src/backend/replication/logical/snapbuild.c
119 : : *
120 : : *-------------------------------------------------------------------------
121 : : */
122 : :
123 : : #include "postgres.h"
124 : :
125 : : #include <sys/stat.h>
126 : : #include <unistd.h>
127 : :
128 : : #include "access/heapam_xlog.h"
129 : : #include "access/transam.h"
130 : : #include "access/xact.h"
131 : : #include "common/file_utils.h"
132 : : #include "miscadmin.h"
133 : : #include "pgstat.h"
134 : : #include "replication/logical.h"
135 : : #include "replication/reorderbuffer.h"
136 : : #include "replication/snapbuild.h"
137 : : #include "replication/snapbuild_internal.h"
138 : : #include "storage/fd.h"
139 : : #include "storage/lmgr.h"
140 : : #include "storage/proc.h"
141 : : #include "storage/procarray.h"
142 : : #include "storage/standby.h"
143 : : #include "utils/builtins.h"
144 : : #include "utils/memutils.h"
145 : : #include "utils/snapmgr.h"
146 : : #include "utils/snapshot.h"
147 : : #include "utils/wait_event.h"
148 : :
149 : :
150 : : /*
151 : : * Starting a transaction -- which we need to do while exporting a snapshot --
152 : : * removes knowledge about the previously used resowner, so we save it here.
153 : : */
154 : : static ResourceOwner SavedResourceOwnerDuringExport = NULL;
155 : : static bool ExportInProgress = false;
156 : :
157 : : /*
158 : : * If a backend is going to do logical decoding and the output plugin does
159 : : * not need to access shared catalogs, setting this variable to false can make
160 : : * the decoding startup faster. In particular, the backend will not need to
161 : : * wait for completion of already running transactions in other databases.
162 : : */
163 : : bool accessSharedCatalogsInDecoding = true;
164 : :
165 : : /* ->committed and ->catchange manipulation */
166 : : static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
167 : :
168 : : /* snapshot building/manipulation/distribution functions */
169 : : static Snapshot SnapBuildBuildSnapshot(SnapBuild *builder);
170 : :
171 : : static void SnapBuildFreeSnapshot(Snapshot snap);
172 : :
173 : : static void SnapBuildSnapIncRefcount(Snapshot snap);
174 : :
175 : : static void SnapBuildDistributeSnapshotAndInval(SnapBuild *builder, XLogRecPtr lsn, TransactionId xid);
176 : :
177 : : static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
178 : : uint32 xinfo);
179 : :
180 : : /* xlog reading helper functions for SnapBuildProcessRunningXacts */
181 : : static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
182 : : xl_running_xacts *running);
183 : : static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
184 : :
185 : : /* serialization functions */
186 : : static void SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn);
187 : : static bool SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn);
188 : : static void SnapBuildRestoreContents(int fd, void *dest, Size size, const char *path);
189 : :
190 : : /*
191 : : * Allocate a new snapshot builder.
192 : : *
193 : : * xmin_horizon is the xid >= which we can be sure no catalog rows have been
194 : : * removed, start_lsn is the LSN >= we want to replay commits.
195 : : */
196 : : SnapBuild *
4446 rhaas@postgresql.org 197 :CBC 1186 : AllocateSnapshotBuilder(ReorderBuffer *reorder,
198 : : TransactionId xmin_horizon,
199 : : XLogRecPtr start_lsn,
200 : : bool need_full_snapshot,
201 : : bool in_slot_creation,
202 : : XLogRecPtr two_phase_at)
203 : : {
204 : : MemoryContext context;
205 : : MemoryContext oldcontext;
206 : : SnapBuild *builder;
207 : :
208 : : /* allocate memory in own context, to have better accountability */
209 : 1186 : context = AllocSetContextCreate(CurrentMemoryContext,
210 : : "snapshot builder context",
211 : : ALLOCSET_DEFAULT_SIZES);
212 : 1186 : oldcontext = MemoryContextSwitchTo(context);
213 : :
146 michael@paquier.xyz 214 :GNC 1186 : builder = palloc0_object(SnapBuild);
215 : :
4446 rhaas@postgresql.org 216 :CBC 1186 : builder->state = SNAPBUILD_START;
217 : 1186 : builder->context = context;
218 : 1186 : builder->reorder = reorder;
219 : : /* Other struct members initialized by zeroing via palloc0 above */
220 : :
221 : 1186 : builder->committed.xcnt = 0;
3240 tgl@sss.pgh.pa.us 222 : 1186 : builder->committed.xcnt_space = 128; /* arbitrary number */
4446 rhaas@postgresql.org 223 : 1186 : builder->committed.xip =
60 msawada@postgresql.o 224 :GNC 1186 : palloc0_array(TransactionId, builder->committed.xcnt_space);
4446 rhaas@postgresql.org 225 :CBC 1186 : builder->committed.includes_all_transactions = true;
226 : :
1363 akapila@postgresql.o 227 : 1186 : builder->catchange.xcnt = 0;
228 : 1186 : builder->catchange.xip = NULL;
229 : :
4446 rhaas@postgresql.org 230 : 1186 : builder->initial_xmin_horizon = xmin_horizon;
4352 andres@anarazel.de 231 : 1186 : builder->start_decoding_at = start_lsn;
663 msawada@postgresql.o 232 : 1186 : builder->in_slot_creation = in_slot_creation;
3295 andres@anarazel.de 233 : 1186 : builder->building_full_snapshot = need_full_snapshot;
1756 akapila@postgresql.o 234 : 1186 : builder->two_phase_at = two_phase_at;
235 : :
4446 rhaas@postgresql.org 236 : 1186 : MemoryContextSwitchTo(oldcontext);
237 : :
238 : : /* The default is that shared catalog are used. */
28 alvherre@kurilemu.de 239 :GNC 1186 : accessSharedCatalogsInDecoding = true;
240 : :
4446 rhaas@postgresql.org 241 :CBC 1186 : return builder;
242 : : }
243 : :
244 : : /*
245 : : * Free a snapshot builder.
246 : : */
247 : : void
248 : 938 : FreeSnapshotBuilder(SnapBuild *builder)
249 : : {
250 : 938 : MemoryContext context = builder->context;
251 : :
252 : : /* free snapshot explicitly, that contains some error checking */
253 [ + + ]: 938 : if (builder->snapshot != NULL)
254 : : {
255 : 226 : SnapBuildSnapDecRefcount(builder->snapshot);
256 : 226 : builder->snapshot = NULL;
257 : : }
258 : :
259 : : /* The default is that shared catalog are used. */
28 alvherre@kurilemu.de 260 :GNC 938 : accessSharedCatalogsInDecoding = true;
261 : :
262 : : /* other resources are deallocated via memory context reset */
4446 rhaas@postgresql.org 263 :CBC 938 : MemoryContextDelete(context);
264 : 938 : }
265 : :
266 : : /*
267 : : * Free an unreferenced snapshot that has previously been built by us.
268 : : */
269 : : static void
270 : 1685 : SnapBuildFreeSnapshot(Snapshot snap)
271 : : {
272 : : /* make sure we don't get passed an external snapshot */
2661 andres@anarazel.de 273 [ - + ]: 1685 : Assert(snap->snapshot_type == SNAPSHOT_HISTORIC_MVCC);
274 : :
275 : : /* make sure nobody modified our snapshot */
4446 rhaas@postgresql.org 276 [ - + ]: 1685 : Assert(snap->curcid == FirstCommandId);
277 [ - + ]: 1685 : Assert(!snap->suboverflowed);
278 [ - + ]: 1685 : Assert(!snap->takenDuringRecovery);
4037 heikki.linnakangas@i 279 [ - + ]: 1685 : Assert(snap->regd_count == 0);
280 : :
281 : : /* slightly more likely, so it's checked even without c-asserts */
4446 rhaas@postgresql.org 282 [ - + ]: 1685 : if (snap->copied)
4446 rhaas@postgresql.org 283 [ # # ]:UBC 0 : elog(ERROR, "cannot free a copied snapshot");
284 : :
4446 rhaas@postgresql.org 285 [ - + ]:CBC 1685 : if (snap->active_count)
4446 rhaas@postgresql.org 286 [ # # ]:UBC 0 : elog(ERROR, "cannot free an active snapshot");
287 : :
4446 rhaas@postgresql.org 288 :CBC 1685 : pfree(snap);
289 : 1685 : }
290 : :
291 : : /*
292 : : * In which state of snapshot building are we?
293 : : */
294 : : SnapBuildState
295 : 2235528 : SnapBuildCurrentState(SnapBuild *builder)
296 : : {
297 : 2235528 : return builder->state;
298 : : }
299 : :
300 : : /*
301 : : * Return the LSN at which the two-phase decoding was first enabled.
302 : : */
303 : : XLogRecPtr
1756 akapila@postgresql.o 304 : 35 : SnapBuildGetTwoPhaseAt(SnapBuild *builder)
305 : : {
306 : 35 : return builder->two_phase_at;
307 : : }
308 : :
309 : : /*
310 : : * Set the LSN at which two-phase decoding is enabled.
311 : : */
312 : : void
313 : 8 : SnapBuildSetTwoPhaseAt(SnapBuild *builder, XLogRecPtr ptr)
314 : : {
315 : 8 : builder->two_phase_at = ptr;
1891 316 : 8 : }
317 : :
318 : : /*
319 : : * Should the contents of transaction ending at 'ptr' be decoded?
320 : : */
321 : : bool
4446 rhaas@postgresql.org 322 : 563852 : SnapBuildXactNeedsSkip(SnapBuild *builder, XLogRecPtr ptr)
323 : : {
4352 andres@anarazel.de 324 : 563852 : return ptr < builder->start_decoding_at;
325 : : }
326 : :
327 : : /*
328 : : * Increase refcount of a snapshot.
329 : : *
330 : : * This is used when handing out a snapshot to some external resource or when
331 : : * adding a Snapshot as builder->snapshot.
332 : : */
333 : : static void
4446 rhaas@postgresql.org 334 : 7323 : SnapBuildSnapIncRefcount(Snapshot snap)
335 : : {
336 : 7323 : snap->active_count++;
337 : 7323 : }
338 : :
339 : : /*
340 : : * Decrease refcount of a snapshot and free if the refcount reaches zero.
341 : : *
342 : : * Externally visible, so that external resources that have been handed an
343 : : * IncRef'ed Snapshot can adjust its refcount easily.
344 : : */
345 : : void
346 : 7045 : SnapBuildSnapDecRefcount(Snapshot snap)
347 : : {
348 : : /* make sure we don't get passed an external snapshot */
2661 andres@anarazel.de 349 [ - + ]: 7045 : Assert(snap->snapshot_type == SNAPSHOT_HISTORIC_MVCC);
350 : :
351 : : /* make sure nobody modified our snapshot */
4446 rhaas@postgresql.org 352 [ - + ]: 7045 : Assert(snap->curcid == FirstCommandId);
353 [ - + ]: 7045 : Assert(!snap->suboverflowed);
354 [ - + ]: 7045 : Assert(!snap->takenDuringRecovery);
355 : :
4037 heikki.linnakangas@i 356 [ - + ]: 7045 : Assert(snap->regd_count == 0);
357 : :
358 [ - + ]: 7045 : Assert(snap->active_count > 0);
359 : :
360 : : /* slightly more likely, so it's checked even without casserts */
4446 rhaas@postgresql.org 361 [ - + ]: 7045 : if (snap->copied)
4446 rhaas@postgresql.org 362 [ # # ]:UBC 0 : elog(ERROR, "cannot free a copied snapshot");
363 : :
4446 rhaas@postgresql.org 364 :CBC 7045 : snap->active_count--;
4037 heikki.linnakangas@i 365 [ + + ]: 7045 : if (snap->active_count == 0)
4446 rhaas@postgresql.org 366 : 1685 : SnapBuildFreeSnapshot(snap);
367 : 7045 : }
368 : :
369 : : /*
370 : : * Build a new snapshot, based on currently committed catalog-modifying
371 : : * transactions.
372 : : *
373 : : * In-progress transactions with catalog access are *not* allowed to modify
374 : : * these snapshots; they have to copy them and fill in appropriate ->curcid
375 : : * and ->subxip/subxcnt values.
376 : : */
377 : : static Snapshot
3247 andres@anarazel.de 378 : 2162 : SnapBuildBuildSnapshot(SnapBuild *builder)
379 : : {
380 : : Snapshot snapshot;
381 : : Size ssize;
382 : :
4446 rhaas@postgresql.org 383 [ - + ]: 2162 : Assert(builder->state >= SNAPBUILD_FULL_SNAPSHOT);
384 : :
385 : 2162 : ssize = sizeof(SnapshotData)
386 : 2162 : + sizeof(TransactionId) * builder->committed.xcnt
387 : 2162 : + sizeof(TransactionId) * 1 /* toplevel xid */ ;
388 : :
389 : 2162 : snapshot = MemoryContextAllocZero(builder->context, ssize);
390 : :
2661 andres@anarazel.de 391 : 2162 : snapshot->snapshot_type = SNAPSHOT_HISTORIC_MVCC;
392 : :
393 : : /*
394 : : * We misuse the original meaning of SnapshotData's xip and subxip fields
395 : : * to make the more fitting for our needs.
396 : : *
397 : : * In the 'xip' array we store transactions that have to be treated as
398 : : * committed. Since we will only ever look at tuples from transactions
399 : : * that have modified the catalog it's more efficient to store those few
400 : : * that exist between xmin and xmax (frequently there are none).
401 : : *
402 : : * Snapshots that are used in transactions that have modified the catalog
403 : : * also use the 'subxip' array to store their toplevel xid and all the
404 : : * subtransaction xids so we can recognize when we need to treat rows as
405 : : * visible that are not in xip but still need to be visible. Subxip only
406 : : * gets filled when the transaction is copied into the context of a
407 : : * catalog modifying transaction since we otherwise share a snapshot
408 : : * between transactions. As long as a txn hasn't modified the catalog it
409 : : * doesn't need to treat any uncommitted rows as visible, so there is no
410 : : * need for those xids.
411 : : *
412 : : * Both arrays are qsort'ed so that we can use bsearch() on them.
413 : : */
4446 rhaas@postgresql.org 414 [ - + ]: 2162 : Assert(TransactionIdIsNormal(builder->xmin));
415 [ - + ]: 2162 : Assert(TransactionIdIsNormal(builder->xmax));
416 : :
417 : 2162 : snapshot->xmin = builder->xmin;
418 : 2162 : snapshot->xmax = builder->xmax;
419 : :
420 : : /* store all transactions to be treated as committed by this snapshot */
421 : 2162 : snapshot->xip =
422 : 2162 : (TransactionId *) ((char *) snapshot + sizeof(SnapshotData));
423 : 2162 : snapshot->xcnt = builder->committed.xcnt;
424 : 2162 : memcpy(snapshot->xip,
425 : 2162 : builder->committed.xip,
426 : 2162 : builder->committed.xcnt * sizeof(TransactionId));
427 : :
428 : : /* sort so we can bsearch() */
429 : 2162 : qsort(snapshot->xip, snapshot->xcnt, sizeof(TransactionId), xidComparator);
430 : :
431 : : /*
432 : : * Initially, subxip is empty, i.e. it's a snapshot to be used by
433 : : * transactions that don't modify the catalog. Will be filled by
434 : : * ReorderBufferCopySnap() if necessary.
435 : : */
436 : 2162 : snapshot->subxcnt = 0;
437 : 2162 : snapshot->subxip = NULL;
438 : :
439 : 2162 : snapshot->suboverflowed = false;
440 : 2162 : snapshot->takenDuringRecovery = false;
441 : 2162 : snapshot->copied = false;
442 : 2162 : snapshot->curcid = FirstCommandId;
443 : 2162 : snapshot->active_count = 0;
4037 heikki.linnakangas@i 444 : 2162 : snapshot->regd_count = 0;
2087 andres@anarazel.de 445 : 2162 : snapshot->snapXactCompletionCount = 0;
446 : :
4446 rhaas@postgresql.org 447 : 2162 : return snapshot;
448 : : }
449 : :
450 : : /*
451 : : * Build the initial slot snapshot and convert it to a normal snapshot that
452 : : * is understood by HeapTupleSatisfiesMVCC.
453 : : *
454 : : * The snapshot will be usable directly in current transaction or exported
455 : : * for loading in different transaction.
456 : : */
457 : : Snapshot
3327 tgl@sss.pgh.pa.us 458 : 216 : SnapBuildInitialSnapshot(SnapBuild *builder)
459 : : {
460 : : Snapshot snap;
461 : : TransactionId xid;
462 : : TransactionId safeXid;
463 : : TransactionId *newxip;
4446 rhaas@postgresql.org 464 : 216 : int newxcnt = 0;
465 : :
3327 tgl@sss.pgh.pa.us 466 [ - + ]: 216 : Assert(XactIsoLevel == XACT_REPEATABLE_READ);
1261 akapila@postgresql.o 467 [ - + ]: 216 : Assert(builder->building_full_snapshot);
468 : :
469 : : /* don't allow older snapshots */
1082 tgl@sss.pgh.pa.us 470 : 216 : InvalidateCatalogSnapshot(); /* about to overwrite MyProc->xmin */
1261 akapila@postgresql.o 471 [ - + ]: 216 : if (HaveRegisteredOrActiveSnapshot())
1261 akapila@postgresql.o 472 [ # # ]:UBC 0 : elog(ERROR, "cannot build an initial slot snapshot when snapshots exist");
1261 akapila@postgresql.o 473 [ - + ]:CBC 216 : Assert(!HistoricSnapshotActive());
474 : :
4446 rhaas@postgresql.org 475 [ - + ]: 216 : if (builder->state != SNAPBUILD_CONSISTENT)
3330 peter_e@gmx.net 476 [ # # ]:UBC 0 : elog(ERROR, "cannot build an initial slot snapshot before reaching a consistent state");
477 : :
4446 rhaas@postgresql.org 478 [ - + ]:CBC 216 : if (!builder->committed.includes_all_transactions)
3330 peter_e@gmx.net 479 [ # # ]:UBC 0 : elog(ERROR, "cannot build an initial slot snapshot, not all transactions are monitored anymore");
480 : :
481 : : /* so we don't overwrite the existing value */
2091 andres@anarazel.de 482 [ - + ]:CBC 216 : if (TransactionIdIsValid(MyProc->xmin))
2091 andres@anarazel.de 483 [ # # ]:UBC 0 : elog(ERROR, "cannot build an initial slot snapshot when MyProc->xmin already is valid");
484 : :
3247 andres@anarazel.de 485 :CBC 216 : snap = SnapBuildBuildSnapshot(builder);
486 : :
487 : : /*
488 : : * We know that snap->xmin is alive, enforced by the logical xmin
489 : : * mechanism. Due to that we can do this without locks, we're only
490 : : * changing our own value.
491 : : *
492 : : * Building an initial snapshot is expensive and an unenforced xmin
493 : : * horizon would have bad consequences, therefore always double-check that
494 : : * the horizon is enforced.
495 : : */
1261 akapila@postgresql.o 496 : 216 : LWLockAcquire(ProcArrayLock, LW_SHARED);
497 : 216 : safeXid = GetOldestSafeDecodingTransactionId(false);
498 : 216 : LWLockRelease(ProcArrayLock);
499 : :
500 [ - + ]: 216 : if (TransactionIdFollows(safeXid, snap->xmin))
1261 akapila@postgresql.o 501 [ # # ]:UBC 0 : elog(ERROR, "cannot build an initial slot snapshot as oldest safe xid %u follows snapshot's xmin %u",
502 : : safeXid, snap->xmin);
503 : :
2091 andres@anarazel.de 504 :CBC 216 : MyProc->xmin = snap->xmin;
505 : :
506 : : /* allocate in transaction context */
146 michael@paquier.xyz 507 :GNC 216 : newxip = palloc_array(TransactionId, GetMaxSnapshotXidCount());
508 : :
509 : : /*
510 : : * snapbuild.c builds transactions in an "inverted" manner, which means it
511 : : * stores committed transactions in ->xip, not ones in progress. Build a
512 : : * classical snapshot by marking all non-committed transactions as
513 : : * in-progress. This can be expensive.
514 : : */
4446 rhaas@postgresql.org 515 [ + - - + :CBC 216 : for (xid = snap->xmin; NormalTransactionIdPrecedes(xid, snap->xmax);)
- + ]
516 : : {
517 : : void *test;
518 : :
519 : : /*
520 : : * Check whether transaction committed using the decoding snapshot
521 : : * meaning of ->xip.
522 : : */
4446 rhaas@postgresql.org 523 :UBC 0 : test = bsearch(&xid, snap->xip, snap->xcnt,
524 : : sizeof(TransactionId), xidComparator);
525 : :
526 [ # # ]: 0 : if (test == NULL)
527 : : {
528 [ # # ]: 0 : if (newxcnt >= GetMaxSnapshotXidCount())
3330 peter_e@gmx.net 529 [ # # ]: 0 : ereport(ERROR,
530 : : (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
531 : : errmsg("initial slot snapshot too large")));
532 : :
4446 rhaas@postgresql.org 533 : 0 : newxip[newxcnt++] = xid;
534 : : }
535 : :
536 [ # # ]: 0 : TransactionIdAdvance(xid);
537 : : }
538 : :
539 : : /* adjust remaining snapshot fields as needed */
2631 michael@paquier.xyz 540 :CBC 216 : snap->snapshot_type = SNAPSHOT_MVCC;
4446 rhaas@postgresql.org 541 : 216 : snap->xcnt = newxcnt;
542 : 216 : snap->xip = newxip;
543 : :
3330 peter_e@gmx.net 544 : 216 : return snap;
545 : : }
546 : :
547 : : /*
548 : : * Export a snapshot so it can be set in another session with SET TRANSACTION
549 : : * SNAPSHOT.
550 : : *
551 : : * For that we need to start a transaction in the current backend as the
552 : : * importing side checks whether the source transaction is still open to make
553 : : * sure the xmin horizon hasn't advanced since then.
554 : : */
555 : : const char *
556 : 1 : SnapBuildExportSnapshot(SnapBuild *builder)
557 : : {
558 : : Snapshot snap;
559 : : char *snapname;
560 : :
561 [ - + ]: 1 : if (IsTransactionOrTransactionBlock())
3330 peter_e@gmx.net 562 [ # # ]:UBC 0 : elog(ERROR, "cannot export a snapshot from within a transaction");
563 : :
3330 peter_e@gmx.net 564 [ - + ]:CBC 1 : if (SavedResourceOwnerDuringExport)
3330 peter_e@gmx.net 565 [ # # ]:UBC 0 : elog(ERROR, "can only export one snapshot at a time");
566 : :
3330 peter_e@gmx.net 567 :CBC 1 : SavedResourceOwnerDuringExport = CurrentResourceOwner;
568 : 1 : ExportInProgress = true;
569 : :
570 : 1 : StartTransactionCommand();
571 : :
572 : : /* There doesn't seem to a nice API to set these */
573 : 1 : XactIsoLevel = XACT_REPEATABLE_READ;
574 : 1 : XactReadOnly = true;
575 : :
3327 tgl@sss.pgh.pa.us 576 : 1 : snap = SnapBuildInitialSnapshot(builder);
577 : :
578 : : /*
579 : : * now that we've built a plain snapshot, make it active and use the
580 : : * normal mechanisms for exporting it
581 : : */
4446 rhaas@postgresql.org 582 : 1 : snapname = ExportSnapshot(snap);
583 : :
584 [ + - ]: 1 : ereport(LOG,
585 : : (errmsg_plural("exported logical decoding snapshot: \"%s\" with %u transaction ID",
586 : : "exported logical decoding snapshot: \"%s\" with %u transaction IDs",
587 : : snap->xcnt,
588 : : snapname, snap->xcnt)));
589 : 1 : return snapname;
590 : : }
591 : :
592 : : /*
593 : : * Ensure there is a snapshot and if not build one for current transaction.
594 : : */
595 : : Snapshot
1317 akapila@postgresql.o 596 : 8 : SnapBuildGetOrBuildSnapshot(SnapBuild *builder)
597 : : {
3681 simon@2ndQuadrant.co 598 [ - + ]: 8 : Assert(builder->state == SNAPBUILD_CONSISTENT);
599 : :
600 : : /* only build a new snapshot if we don't have a prebuilt one */
601 [ + + ]: 8 : if (builder->snapshot == NULL)
602 : : {
3247 andres@anarazel.de 603 : 1 : builder->snapshot = SnapBuildBuildSnapshot(builder);
604 : : /* increase refcount for the snapshot builder */
3681 simon@2ndQuadrant.co 605 : 1 : SnapBuildSnapIncRefcount(builder->snapshot);
606 : : }
607 : :
608 : 8 : return builder->snapshot;
609 : : }
610 : :
611 : : /*
612 : : * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
613 : : * any. Aborts the previously started transaction and resets the resource
614 : : * owner back to its original value.
615 : : */
616 : : void
3916 andres@anarazel.de 617 : 5810 : SnapBuildClearExportedSnapshot(void)
618 : : {
619 : : ResourceOwner tmpResOwner;
620 : :
621 : : /* nothing exported, that is the usual case */
4446 rhaas@postgresql.org 622 [ + + ]: 5810 : if (!ExportInProgress)
623 : 5809 : return;
624 : :
625 [ - + ]: 1 : if (!IsTransactionState())
4446 rhaas@postgresql.org 626 [ # # ]:UBC 0 : elog(ERROR, "clearing exported snapshot in wrong transaction state");
627 : :
628 : : /*
629 : : * AbortCurrentTransaction() takes care of resetting the snapshot state,
630 : : * so remember SavedResourceOwnerDuringExport.
631 : : */
1660 michael@paquier.xyz 632 :CBC 1 : tmpResOwner = SavedResourceOwnerDuringExport;
633 : :
634 : : /* make sure nothing could have ever happened */
4446 rhaas@postgresql.org 635 : 1 : AbortCurrentTransaction();
636 : :
1660 michael@paquier.xyz 637 : 1 : CurrentResourceOwner = tmpResOwner;
638 : : }
639 : :
640 : : /*
641 : : * Clear snapshot export state during transaction abort.
642 : : */
643 : : void
644 : 35353 : SnapBuildResetExportedSnapshotState(void)
645 : : {
4446 rhaas@postgresql.org 646 : 35353 : SavedResourceOwnerDuringExport = NULL;
647 : 35353 : ExportInProgress = false;
648 : 35353 : }
649 : :
650 : : /*
651 : : * Handle the effects of a single heap change, appropriate to the current state
652 : : * of the snapshot builder and returns whether changes made at (xid, lsn) can
653 : : * be decoded.
654 : : */
655 : : bool
656 : 1446607 : SnapBuildProcessChange(SnapBuild *builder, TransactionId xid, XLogRecPtr lsn)
657 : : {
658 : : /*
659 : : * We can't handle data in transactions if we haven't built a snapshot
660 : : * yet, so don't store them.
661 : : */
662 [ - + ]: 1446607 : if (builder->state < SNAPBUILD_FULL_SNAPSHOT)
4446 rhaas@postgresql.org 663 :UBC 0 : return false;
664 : :
665 : : /*
666 : : * No point in keeping track of changes in transactions that we don't have
667 : : * enough information about to decode. This means that they started before
668 : : * we got into the SNAPBUILD_FULL_SNAPSHOT state.
669 : : */
4446 rhaas@postgresql.org 670 [ + + - + ]:CBC 1446610 : if (builder->state < SNAPBUILD_CONSISTENT &&
1905 andres@anarazel.de 671 : 3 : TransactionIdPrecedes(xid, builder->next_phase_at))
4446 rhaas@postgresql.org 672 :UBC 0 : return false;
673 : :
674 : : /*
675 : : * If the reorderbuffer doesn't yet have a snapshot, add one now, it will
676 : : * be needed to decode the change we're currently processing.
677 : : */
3713 andres@anarazel.de 678 [ + + ]:CBC 1446607 : if (!ReorderBufferXidHasBaseSnapshot(builder->reorder, xid))
679 : : {
680 : : /* only build a new snapshot if we don't have a prebuilt one */
4446 rhaas@postgresql.org 681 [ + + ]: 3861 : if (builder->snapshot == NULL)
682 : : {
3247 andres@anarazel.de 683 : 433 : builder->snapshot = SnapBuildBuildSnapshot(builder);
684 : : /* increase refcount for the snapshot builder */
4446 rhaas@postgresql.org 685 : 433 : SnapBuildSnapIncRefcount(builder->snapshot);
686 : : }
687 : :
688 : : /*
689 : : * Increase refcount for the transaction we're handing the snapshot
690 : : * out to.
691 : : */
692 : 3861 : SnapBuildSnapIncRefcount(builder->snapshot);
693 : 3861 : ReorderBufferSetBaseSnapshot(builder->reorder, xid, lsn,
694 : : builder->snapshot);
695 : : }
696 : :
697 : 1446607 : return true;
698 : : }
699 : :
700 : : /*
701 : : * Do CommandId/combo CID handling after reading an xl_heap_new_cid record.
702 : : * This implies that a transaction has done some form of write to system
703 : : * catalogs.
704 : : */
705 : : void
706 : 26781 : SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
707 : : XLogRecPtr lsn, xl_heap_new_cid *xlrec)
708 : : {
709 : : CommandId cid;
710 : :
711 : : /*
712 : : * we only log new_cid's if a catalog tuple was modified, so mark the
713 : : * transaction as containing catalog modifications
714 : : */
4382 bruce@momjian.us 715 : 26781 : ReorderBufferXidSetCatalogChanges(builder->reorder, xid, lsn);
716 : :
4446 rhaas@postgresql.org 717 : 26781 : ReorderBufferAddNewTupleCids(builder->reorder, xlrec->top_xid, lsn,
718 : : xlrec->target_locator, xlrec->target_tid,
719 : : xlrec->cmin, xlrec->cmax,
720 : : xlrec->combocid);
721 : :
722 : : /* figure out new command id */
723 [ + + ]: 26781 : if (xlrec->cmin != InvalidCommandId &&
724 [ + + ]: 22413 : xlrec->cmax != InvalidCommandId)
725 : 3295 : cid = Max(xlrec->cmin, xlrec->cmax);
726 [ + + ]: 23486 : else if (xlrec->cmax != InvalidCommandId)
727 : 4368 : cid = xlrec->cmax;
728 [ + - ]: 19118 : else if (xlrec->cmin != InvalidCommandId)
729 : 19118 : cid = xlrec->cmin;
730 : : else
731 : : {
4382 bruce@momjian.us 732 :UBC 0 : cid = InvalidCommandId; /* silence compiler */
4446 rhaas@postgresql.org 733 [ # # ]: 0 : elog(ERROR, "xl_heap_new_cid record without a valid CommandId");
734 : : }
735 : :
4446 rhaas@postgresql.org 736 :CBC 26781 : ReorderBufferAddNewCommandId(builder->reorder, xid, lsn, cid + 1);
737 : 26781 : }
738 : :
739 : : /*
740 : : * Add a new Snapshot and invalidation messages to all transactions we're
741 : : * decoding that currently are in-progress so they can see new catalog contents
742 : : * made by the transaction that just committed. This is necessary because those
743 : : * in-progress transactions will use the new catalog's contents from here on
744 : : * (at the very least everything they do needs to be compatible with newer
745 : : * catalog contents).
746 : : */
747 : : static void
390 akapila@postgresql.o 748 : 1503 : SnapBuildDistributeSnapshotAndInval(SnapBuild *builder, XLogRecPtr lsn, TransactionId xid)
749 : : {
750 : : dlist_iter txn_i;
751 : : ReorderBufferTXN *txn;
752 : :
753 : : /*
754 : : * Iterate through all toplevel transactions. This can include
755 : : * subtransactions which we just don't yet know to be that, but that's
756 : : * fine, they will just get an unnecessary snapshot and invalidations
757 : : * queued.
758 : : */
4446 rhaas@postgresql.org 759 [ + - + + ]: 3041 : dlist_foreach(txn_i, &builder->reorder->toplevel_by_lsn)
760 : : {
761 : 1538 : txn = dlist_container(ReorderBufferTXN, node, txn_i.cur);
762 : :
763 [ - + ]: 1538 : Assert(TransactionIdIsValid(txn->xid));
764 : :
765 : : /*
766 : : * If we don't have a base snapshot yet, there are no changes in this
767 : : * transaction which in turn implies we don't yet need a snapshot at
768 : : * all. We'll add a snapshot when the first change gets queued.
769 : : *
770 : : * Similarly, we don't need to add invalidations to a transaction
771 : : * whose base snapshot is not yet set. Once a base snapshot is built,
772 : : * it will include the xids of committed transactions that have
773 : : * modified the catalog, thus reflecting the new catalog contents. The
774 : : * existing catalog cache will have already been invalidated after
775 : : * processing the invalidations in the transaction that modified
776 : : * catalogs, ensuring that a fresh cache is constructed during
777 : : * decoding.
778 : : *
779 : : * NB: This works correctly even for subtransactions because
780 : : * ReorderBufferAssignChild() takes care to transfer the base snapshot
781 : : * to the top-level transaction, and while iterating the changequeue
782 : : * we'll get the change from the subtxn.
783 : : */
784 [ + + ]: 1538 : if (!ReorderBufferXidHasBaseSnapshot(builder->reorder, txn->xid))
785 : 2 : continue;
786 : :
787 : : /*
788 : : * We don't need to add snapshot or invalidations to prepared
789 : : * transactions as they should not see the new catalog contents.
790 : : */
447 msawada@postgresql.o 791 [ + + ]: 1536 : if (rbtxn_is_prepared(txn))
1947 akapila@postgresql.o 792 : 28 : continue;
793 : :
302 alvherre@kurilemu.de 794 [ + + ]:GNC 1508 : elog(DEBUG2, "adding a new snapshot and invalidations to %u at %X/%08X",
795 : : txn->xid, LSN_FORMAT_ARGS(lsn));
796 : :
797 : : /*
798 : : * increase the snapshot's refcount for the transaction we are handing
799 : : * it out to
800 : : */
4446 rhaas@postgresql.org 801 :CBC 1508 : SnapBuildSnapIncRefcount(builder->snapshot);
802 : 1508 : ReorderBufferAddSnapshot(builder->reorder, txn->xid, lsn,
803 : : builder->snapshot);
804 : :
805 : : /*
806 : : * Add invalidation messages to the reorder buffer of in-progress
807 : : * transactions except the current committed transaction, for which we
808 : : * will execute invalidations at the end.
809 : : *
810 : : * It is required, otherwise, we will end up using the stale catcache
811 : : * contents built by the current transaction even after its decoding,
812 : : * which should have been invalidated due to concurrent catalog
813 : : * changing transaction.
814 : : *
815 : : * Distribute only the invalidation messages generated by the current
816 : : * committed transaction. Invalidation messages received from other
817 : : * transactions would have already been propagated to the relevant
818 : : * in-progress transactions. This transaction would have processed
819 : : * those invalidations, ensuring that subsequent transactions observe
820 : : * a consistent cache state.
821 : : */
390 akapila@postgresql.o 822 [ + + ]: 1508 : if (txn->xid != xid)
823 : : {
824 : : uint32 ninvalidations;
825 : 33 : SharedInvalidationMessage *msgs = NULL;
826 : :
827 : 33 : ninvalidations = ReorderBufferGetInvalidations(builder->reorder,
828 : : xid, &msgs);
829 : :
830 [ + + ]: 33 : if (ninvalidations > 0)
831 : : {
832 [ - + ]: 29 : Assert(msgs != NULL);
833 : :
323 msawada@postgresql.o 834 : 29 : ReorderBufferAddDistributedInvalidations(builder->reorder,
835 : : txn->xid, lsn,
836 : : ninvalidations, msgs);
837 : : }
838 : : }
839 : : }
4446 rhaas@postgresql.org 840 : 1503 : }
841 : :
842 : : /*
843 : : * Keep track of a new catalog changing transaction that has committed.
844 : : */
845 : : static void
846 : 1512 : SnapBuildAddCommittedTxn(SnapBuild *builder, TransactionId xid)
847 : : {
848 [ - + ]: 1512 : Assert(TransactionIdIsValid(xid));
849 : :
850 [ + + ]: 1512 : if (builder->committed.xcnt == builder->committed.xcnt_space)
851 : : {
4446 rhaas@postgresql.org 852 :GBC 1 : builder->committed.xcnt_space = builder->committed.xcnt_space * 2 + 1;
853 : :
854 [ - + ]: 1 : elog(DEBUG1, "increasing space for committed transactions to %u",
855 : : (uint32) builder->committed.xcnt_space);
856 : :
60 msawada@postgresql.o 857 :GNC 1 : builder->committed.xip = repalloc_array(builder->committed.xip,
858 : : TransactionId,
859 : : builder->committed.xcnt_space);
860 : : }
861 : :
862 : : /*
863 : : * TODO: It might make sense to keep the array sorted here instead of
864 : : * doing it every time we build a new snapshot. On the other hand this
865 : : * gets called repeatedly when a transaction with subtransactions commits.
866 : : */
4446 rhaas@postgresql.org 867 :CBC 1512 : builder->committed.xip[builder->committed.xcnt++] = xid;
868 : 1512 : }
869 : :
870 : : /*
871 : : * Remove knowledge about transactions we treat as committed or containing catalog
872 : : * changes that are smaller than ->xmin. Those won't ever get checked via
873 : : * the ->committed or ->catchange array, respectively. The committed xids will
874 : : * get checked via the clog machinery.
875 : : *
876 : : * We can ideally remove the transaction from catchange array once it is
877 : : * finished (committed/aborted) but that could be costly as we need to maintain
878 : : * the xids order in the array.
879 : : */
880 : : static void
1363 akapila@postgresql.o 881 : 507 : SnapBuildPurgeOlderTxn(SnapBuild *builder)
882 : : {
883 : : int off;
884 : : TransactionId *workspace;
4446 rhaas@postgresql.org 885 : 507 : int surviving_xids = 0;
886 : :
887 : : /* not ready yet */
888 [ - + ]: 507 : if (!TransactionIdIsNormal(builder->xmin))
4446 rhaas@postgresql.org 889 :UBC 0 : return;
890 : :
891 : : /* TODO: Neater algorithm than just copying and iterating? */
892 : : workspace =
4446 rhaas@postgresql.org 893 :CBC 507 : MemoryContextAlloc(builder->context,
894 : 507 : builder->committed.xcnt * sizeof(TransactionId));
895 : :
896 : : /* copy xids that still are interesting to workspace */
897 [ + + ]: 801 : for (off = 0; off < builder->committed.xcnt; off++)
898 : : {
899 [ + - - + : 294 : if (NormalTransactionIdPrecedes(builder->committed.xip[off],
+ + ]
900 : : builder->xmin))
901 : : ; /* remove */
902 : : else
903 : 1 : workspace[surviving_xids++] = builder->committed.xip[off];
904 : : }
905 : :
906 : : /* copy workspace back to persistent state */
907 : 507 : memcpy(builder->committed.xip, workspace,
908 : : surviving_xids * sizeof(TransactionId));
909 : :
910 [ - + ]: 507 : elog(DEBUG3, "purged committed transactions from %u to %u, xmin: %u, xmax: %u",
911 : : (uint32) builder->committed.xcnt, (uint32) surviving_xids,
912 : : builder->xmin, builder->xmax);
913 : 507 : builder->committed.xcnt = surviving_xids;
914 : :
915 : 507 : pfree(workspace);
916 : :
917 : : /*
918 : : * Purge xids in ->catchange as well. The purged array must also be sorted
919 : : * in xidComparator order.
920 : : */
1345 akapila@postgresql.o 921 [ + + ]: 507 : if (builder->catchange.xcnt > 0)
922 : : {
923 : : /*
924 : : * Since catchange.xip is sorted, we find the lower bound of xids that
925 : : * are still interesting.
926 : : */
927 [ + + ]: 9 : for (off = 0; off < builder->catchange.xcnt; off++)
928 : : {
929 [ + + ]: 6 : if (TransactionIdFollowsOrEquals(builder->catchange.xip[off],
930 : : builder->xmin))
931 : 1 : break;
932 : : }
933 : :
934 : 4 : surviving_xids = builder->catchange.xcnt - off;
935 : :
936 [ + + ]: 4 : if (surviving_xids > 0)
937 : : {
938 : 1 : memmove(builder->catchange.xip, &(builder->catchange.xip[off]),
939 : : surviving_xids * sizeof(TransactionId));
940 : : }
941 : : else
942 : : {
943 : 3 : pfree(builder->catchange.xip);
944 : 3 : builder->catchange.xip = NULL;
945 : : }
946 : :
947 [ - + ]: 4 : elog(DEBUG3, "purged catalog modifying transactions from %u to %u, xmin: %u, xmax: %u",
948 : : (uint32) builder->catchange.xcnt, (uint32) surviving_xids,
949 : : builder->xmin, builder->xmax);
950 : 4 : builder->catchange.xcnt = surviving_xids;
951 : : }
952 : : }
953 : :
954 : : /*
955 : : * Handle everything that needs to be done when a transaction commits
956 : : */
957 : : void
4446 rhaas@postgresql.org 958 : 3716 : SnapBuildCommitTxn(SnapBuild *builder, XLogRecPtr lsn, TransactionId xid,
959 : : int nsubxacts, TransactionId *subxacts, uint32 xinfo)
960 : : {
961 : : int nxact;
962 : :
3279 andres@anarazel.de 963 : 3716 : bool needs_snapshot = false;
964 : 3716 : bool needs_timetravel = false;
4446 rhaas@postgresql.org 965 : 3716 : bool sub_needs_timetravel = false;
966 : :
967 : 3716 : TransactionId xmax = xid;
968 : :
969 : : /*
970 : : * Transactions preceding BUILDING_SNAPSHOT will neither be decoded, nor
971 : : * will they be part of a snapshot. So we don't need to record anything.
972 : : */
3279 andres@anarazel.de 973 [ + - ]: 3716 : if (builder->state == SNAPBUILD_START ||
974 [ - + - - ]: 3716 : (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
1905 andres@anarazel.de 975 :UBC 0 : TransactionIdPrecedes(xid, builder->next_phase_at)))
976 : : {
977 : : /* ensure that only commits after this are getting replayed */
3279 978 [ # # ]: 0 : if (builder->start_decoding_at <= lsn)
979 : 0 : builder->start_decoding_at = lsn + 1;
980 : 0 : return;
981 : : }
982 : :
4446 rhaas@postgresql.org 983 [ + + ]:CBC 3716 : if (builder->state < SNAPBUILD_CONSISTENT)
984 : : {
985 : : /* ensure that only commits after this are getting replayed */
4352 andres@anarazel.de 986 [ + + ]: 5 : if (builder->start_decoding_at <= lsn)
987 : 2 : builder->start_decoding_at = lsn + 1;
988 : :
989 : : /*
990 : : * If building an exportable snapshot, force xid to be tracked, even
991 : : * if the transaction didn't modify the catalog.
992 : : */
3279 993 [ - + ]: 5 : if (builder->building_full_snapshot)
994 : : {
3279 andres@anarazel.de 995 :UBC 0 : needs_timetravel = true;
996 : : }
997 : : }
998 : :
4446 rhaas@postgresql.org 999 [ + + ]:CBC 4928 : for (nxact = 0; nxact < nsubxacts; nxact++)
1000 : : {
1001 : 1212 : TransactionId subxid = subxacts[nxact];
1002 : :
1003 : : /*
1004 : : * Add subtransaction to base snapshot if catalog modifying, we don't
1005 : : * distinguish to toplevel transactions there.
1006 : : */
1363 akapila@postgresql.o 1007 [ + + ]: 1212 : if (SnapBuildXidHasCatalogChanges(builder, subxid, xinfo))
1008 : : {
3279 andres@anarazel.de 1009 : 9 : sub_needs_timetravel = true;
1010 : 9 : needs_snapshot = true;
1011 : :
1012 [ - + ]: 9 : elog(DEBUG1, "found subtransaction %u:%u with catalog changes",
1013 : : xid, subxid);
1014 : :
4446 rhaas@postgresql.org 1015 : 9 : SnapBuildAddCommittedTxn(builder, subxid);
1016 : :
1017 [ + - - + : 9 : if (NormalTransactionIdFollows(subxid, xmax))
+ - ]
1018 : 9 : xmax = subxid;
1019 : : }
1020 : :
1021 : : /*
1022 : : * If we're forcing timetravel we also need visibility information
1023 : : * about subtransaction, so keep track of subtransaction's state, even
1024 : : * if not catalog modifying. Don't need to distribute a snapshot in
1025 : : * that case.
1026 : : */
3279 andres@anarazel.de 1027 [ - + ]: 1203 : else if (needs_timetravel)
1028 : : {
4446 rhaas@postgresql.org 1029 :UBC 0 : SnapBuildAddCommittedTxn(builder, subxid);
1030 [ # # # # : 0 : if (NormalTransactionIdFollows(subxid, xmax))
# # ]
1031 : 0 : xmax = subxid;
1032 : : }
1033 : : }
1034 : :
1035 : : /* if top-level modified catalog, it'll need a snapshot */
1363 akapila@postgresql.o 1036 [ + + ]:CBC 3716 : if (SnapBuildXidHasCatalogChanges(builder, xid, xinfo))
1037 : : {
3279 andres@anarazel.de 1038 [ + + ]: 1502 : elog(DEBUG2, "found top level transaction %u, with catalog changes",
1039 : : xid);
1040 : 1502 : needs_snapshot = true;
1041 : 1502 : needs_timetravel = true;
4446 rhaas@postgresql.org 1042 : 1502 : SnapBuildAddCommittedTxn(builder, xid);
1043 : : }
3279 andres@anarazel.de 1044 [ + + ]: 2214 : else if (sub_needs_timetravel)
1045 : : {
1046 : : /* track toplevel txn as well, subxact alone isn't meaningful */
1293 akapila@postgresql.o 1047 [ - + ]: 1 : elog(DEBUG2, "forced transaction %u to do timetravel due to one of its subtransactions",
1048 : : xid);
1049 : 1 : needs_timetravel = true;
4446 rhaas@postgresql.org 1050 : 1 : SnapBuildAddCommittedTxn(builder, xid);
1051 : : }
3279 andres@anarazel.de 1052 [ - + ]: 2213 : else if (needs_timetravel)
1053 : : {
3279 andres@anarazel.de 1054 [ # # ]:UBC 0 : elog(DEBUG2, "forced transaction %u to do timetravel", xid);
1055 : :
4446 rhaas@postgresql.org 1056 : 0 : SnapBuildAddCommittedTxn(builder, xid);
1057 : : }
1058 : :
3279 andres@anarazel.de 1059 [ + + ]:CBC 3716 : if (!needs_timetravel)
1060 : : {
1061 : : /* record that we cannot export a general snapshot anymore */
1062 : 2213 : builder->committed.includes_all_transactions = false;
1063 : : }
1064 : :
1065 [ + + - + ]: 3716 : Assert(!needs_snapshot || needs_timetravel);
1066 : :
1067 : : /*
1068 : : * Adjust xmax of the snapshot builder, we only do that for committed,
1069 : : * catalog modifying, transactions, everything else isn't interesting for
1070 : : * us since we'll never look at the respective rows.
1071 : : */
1072 [ + + ]: 3716 : if (needs_timetravel &&
1073 [ + - + + ]: 3006 : (!TransactionIdIsValid(builder->xmax) ||
1074 : 1503 : TransactionIdFollowsOrEquals(xmax, builder->xmax)))
1075 : : {
1076 : 1502 : builder->xmax = xmax;
1077 [ - + ]: 1502 : TransactionIdAdvance(builder->xmax);
1078 : : }
1079 : :
1080 : : /* if there's any reason to build a historic snapshot, do so now */
1081 [ + + ]: 3716 : if (needs_snapshot)
1082 : : {
1083 : : /*
1084 : : * If we haven't built a complete snapshot yet there's no need to hand
1085 : : * it out, it wouldn't (and couldn't) be used anyway.
1086 : : */
4446 rhaas@postgresql.org 1087 [ - + ]: 1503 : if (builder->state < SNAPBUILD_FULL_SNAPSHOT)
4446 rhaas@postgresql.org 1088 :UBC 0 : return;
1089 : :
1090 : : /*
1091 : : * Decrease the snapshot builder's refcount of the old snapshot, note
1092 : : * that it still will be used if it has been handed out to the
1093 : : * reorderbuffer earlier.
1094 : : */
4446 rhaas@postgresql.org 1095 [ + - ]:CBC 1503 : if (builder->snapshot)
1096 : 1503 : SnapBuildSnapDecRefcount(builder->snapshot);
1097 : :
3247 andres@anarazel.de 1098 : 1503 : builder->snapshot = SnapBuildBuildSnapshot(builder);
1099 : :
1100 : : /* we might need to execute invalidations, add snapshot */
4446 rhaas@postgresql.org 1101 [ + + ]: 1503 : if (!ReorderBufferXidHasBaseSnapshot(builder->reorder, xid))
1102 : : {
1103 : 8 : SnapBuildSnapIncRefcount(builder->snapshot);
1104 : 8 : ReorderBufferSetBaseSnapshot(builder->reorder, xid, lsn,
1105 : : builder->snapshot);
1106 : : }
1107 : :
1108 : : /* refcount of the snapshot builder for the new snapshot */
1109 : 1503 : SnapBuildSnapIncRefcount(builder->snapshot);
1110 : :
1111 : : /*
1112 : : * Add a new catalog snapshot and invalidations messages to all
1113 : : * currently running transactions.
1114 : : */
390 akapila@postgresql.o 1115 : 1503 : SnapBuildDistributeSnapshotAndInval(builder, lsn, xid);
1116 : : }
1117 : : }
1118 : :
1119 : : /*
1120 : : * Check the reorder buffer and the snapshot to see if the given transaction has
1121 : : * modified catalogs.
1122 : : */
1123 : : static inline bool
1363 1124 : 4928 : SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
1125 : : uint32 xinfo)
1126 : : {
1127 [ + + ]: 4928 : if (ReorderBufferXidHasCatalogChanges(builder->reorder, xid))
1128 : 1507 : return true;
1129 : :
1130 : : /*
1131 : : * The transactions that have changed catalogs must have invalidation
1132 : : * info.
1133 : : */
1134 [ + + ]: 3421 : if (!(xinfo & XACT_XINFO_HAS_INVALS))
1135 : 3413 : return false;
1136 : :
1137 : : /* Check the catchange XID array */
1138 [ + + + - ]: 12 : return ((builder->catchange.xcnt > 0) &&
1139 : 4 : (bsearch(&xid, builder->catchange.xip, builder->catchange.xcnt,
1140 : : sizeof(TransactionId), xidComparator) != NULL));
1141 : : }
1142 : :
1143 : : /* -----------------------------------
1144 : : * Snapshot building functions dealing with xlog records
1145 : : * -----------------------------------
1146 : : */
1147 : :
1148 : : /*
1149 : : * Process a running xacts record, and use its information to first build a
1150 : : * historic snapshot and later to release resources that aren't needed
1151 : : * anymore.
1152 : : */
1153 : : void
28 alvherre@kurilemu.de 1154 :GNC 1653 : SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
1155 : : bool db_specific)
1156 : : {
1157 : : ReorderBufferTXN *txn;
1158 : : TransactionId xmin;
1159 : :
1160 : : /*
1161 : : * If we're not consistent yet, inspect the record to see whether it
1162 : : * allows to get closer to being consistent. If we are consistent, dump
1163 : : * our snapshot so others or we, after a restart, can use it.
1164 : : */
4446 rhaas@postgresql.org 1165 [ + + ]:CBC 1653 : if (builder->state < SNAPBUILD_CONSISTENT)
1166 : : {
1167 : : /*
1168 : : * To reduce the potential for unnecessarily waiting for completion of
1169 : : * unrelated transactions, the caller can declare that only
1170 : : * transactions of the current database are relevant at this stage.
1171 : : */
28 alvherre@kurilemu.de 1172 [ + + ]:GNC 1169 : if (db_specific)
1173 : : {
1174 : : /*
1175 : : * If we must only keep track of transactions running in the
1176 : : * current database, we need transaction info from exactly that
1177 : : * database.
1178 : : */
1179 [ + + ]: 6 : if (running->dbid != MyDatabaseId)
1180 : : {
1181 : 3 : LogStandbySnapshot(MyDatabaseId);
1182 : :
1183 : 3 : return;
1184 : : }
1185 : :
1186 : : /*
1187 : : * We'd better be able to check during scan if the plugin does not
1188 : : * lie.
1189 : : */
1190 [ + - ]: 3 : if (accessSharedCatalogsInDecoding)
1191 : 3 : accessSharedCatalogsInDecoding = false;
1192 : : }
1193 : :
1194 : : /* returns false if there's no point in performing cleanup just yet */
4446 rhaas@postgresql.org 1195 [ + + ]:CBC 1166 : if (!SnapBuildFindSnapshot(builder, lsn, running))
1196 : 1141 : return;
1197 : : }
1198 : : else
1199 : 484 : SnapBuildSerialize(builder, lsn);
1200 : :
1201 : : /*
1202 : : * Database specific transaction info may exist to reach CONSISTENT state
1203 : : * faster, however the code below makes no use of it. Moreover, such
1204 : : * record might cause problems because the following normal (cluster-wide)
1205 : : * record can have lower value of oldestRunningXid. In that case, let's
1206 : : * wait with the cleanup for the next regular cluster-wide record.
1207 : : */
28 alvherre@kurilemu.de 1208 [ - + ]:GNC 507 : if (OidIsValid(running->dbid))
28 alvherre@kurilemu.de 1209 :UNC 0 : return;
1210 : :
1211 : : /*
1212 : : * Update range of interesting xids based on the running xacts
1213 : : * information. We don't increase ->xmax using it, because once we are in
1214 : : * a consistent state we can do that ourselves and much more efficiently
1215 : : * so, because we only need to do it for catalog transactions since we
1216 : : * only ever look at those.
1217 : : *
1218 : : * NB: We only increase xmax when a catalog modifying transaction commits
1219 : : * (see SnapBuildCommitTxn). Because of this, xmax can be lower than
1220 : : * xmin, which looks odd but is correct and actually more efficient, since
1221 : : * we hit fast paths in heapam_visibility.c.
1222 : : */
4446 rhaas@postgresql.org 1223 :CBC 507 : builder->xmin = running->oldestRunningXid;
1224 : :
1225 : : /* Remove transactions we don't need to keep track off anymore */
1363 akapila@postgresql.o 1226 : 507 : SnapBuildPurgeOlderTxn(builder);
1227 : :
1228 : : /*
1229 : : * Advance the xmin limit for the current replication slot, to allow
1230 : : * vacuum to clean up the tuples this slot has been protecting.
1231 : : *
1232 : : * The reorderbuffer might have an xmin among the currently running
1233 : : * snapshots; use it if so. If not, we need only consider the snapshots
1234 : : * we'll produce later, which can't be less than the oldest running xid in
1235 : : * the record we're reading now.
1236 : : */
2870 alvherre@alvh.no-ip. 1237 : 507 : xmin = ReorderBufferGetOldestXmin(builder->reorder);
1238 [ + + ]: 507 : if (xmin == InvalidTransactionId)
1239 : 456 : xmin = running->oldestRunningXid;
1240 [ - + ]: 507 : elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
1241 : : builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
1242 : 507 : LogicalIncreaseXminForSlot(lsn, xmin);
1243 : :
1244 : : /*
1245 : : * Also tell the slot where we can restart decoding from. We don't want to
1246 : : * do that after every commit because changing that implies an fsync of
1247 : : * the logical slot's state file, so we only do it every time we see a
1248 : : * running xacts record.
1249 : : *
1250 : : * Do so by looking for the oldest in progress transaction (determined by
1251 : : * the first LSN of any of its relevant records). Every transaction
1252 : : * remembers the last location we stored the snapshot to disk before its
1253 : : * beginning. That point is where we can restart from.
1254 : : */
1255 : :
1256 : : /*
1257 : : * Can't know about a serialized snapshot's location if we're not
1258 : : * consistent.
1259 : : */
4446 rhaas@postgresql.org 1260 [ + + ]: 507 : if (builder->state < SNAPBUILD_CONSISTENT)
1261 : 18 : return;
1262 : :
1263 : 489 : txn = ReorderBufferGetOldestTXN(builder->reorder);
1264 : :
1265 : : /*
1266 : : * oldest ongoing txn might have started when we didn't yet serialize
1267 : : * anything because we hadn't reached a consistent state yet.
1268 : : */
180 alvherre@kurilemu.de 1269 [ + + + + ]:GNC 489 : if (txn != NULL && XLogRecPtrIsValid(txn->restart_decoding_lsn))
4446 rhaas@postgresql.org 1270 :CBC 25 : LogicalIncreaseRestartDecodingForSlot(lsn, txn->restart_decoding_lsn);
1271 : :
1272 : : /*
1273 : : * No in-progress transaction, can reuse the last serialized snapshot if
1274 : : * we have one.
1275 : : */
1276 [ + + ]: 464 : else if (txn == NULL &&
180 alvherre@kurilemu.de 1277 [ + + ]:GNC 429 : XLogRecPtrIsValid(builder->reorder->current_restart_decoding_lsn) &&
1278 [ + - ]: 427 : XLogRecPtrIsValid(builder->last_serialized_snapshot))
4446 rhaas@postgresql.org 1279 :CBC 427 : LogicalIncreaseRestartDecodingForSlot(lsn,
1280 : : builder->last_serialized_snapshot);
1281 : : }
1282 : :
1283 : :
1284 : : /*
1285 : : * Build the start of a snapshot that's capable of decoding the catalog.
1286 : : *
1287 : : * Helper function for SnapBuildProcessRunningXacts() while we're not yet
1288 : : * consistent.
1289 : : *
1290 : : * Returns true if there is a point in performing internal maintenance/cleanup
1291 : : * using the xl_running_xacts record.
1292 : : */
1293 : : static bool
1294 : 1166 : SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
1295 : : {
1296 : : /* ---
1297 : : * Build catalog decoding snapshot incrementally using information about
1298 : : * the currently running transactions. There are several ways to do that:
1299 : : *
1300 : : * a) There were no running transactions when the xl_running_xacts record
1301 : : * was inserted, jump to CONSISTENT immediately. We might find such a
1302 : : * state while waiting on c)'s sub-states.
1303 : : *
1304 : : * b) This (in a previous run) or another decoding slot serialized a
1305 : : * snapshot to disk that we can use. Can't use this method while finding
1306 : : * the start point for decoding changes as the restart LSN would be an
1307 : : * arbitrary LSN but we need to find the start point to extract changes
1308 : : * where we won't see the data for partial transactions. Also, we cannot
1309 : : * use this method when a slot needs a full snapshot for export or direct
1310 : : * use, as that snapshot will only contain catalog modifying transactions.
1311 : : *
1312 : : * c) First incrementally build a snapshot for catalog tuples
1313 : : * (BUILDING_SNAPSHOT), that requires all, already in-progress,
1314 : : * transactions to finish. Every transaction starting after that
1315 : : * (FULL_SNAPSHOT state), has enough information to be decoded. But
1316 : : * for older running transactions no viable snapshot exists yet, so
1317 : : * CONSISTENT will only be reached once all of those have finished.
1318 : : * ---
1319 : : */
1320 : :
1321 : : /*
1322 : : * xl_running_xacts record is older than what we can use, we might not
1323 : : * have all necessary catalog rows anymore.
1324 : : */
1325 [ + + ]: 1166 : if (TransactionIdIsNormal(builder->initial_xmin_horizon) &&
1326 [ + - - + : 501 : NormalTransactionIdPrecedes(running->oldestRunningXid,
- + ]
1327 : : builder->initial_xmin_horizon))
1328 : : {
4446 rhaas@postgresql.org 1329 [ # # ]:UBC 0 : ereport(DEBUG1,
1330 : : errmsg_internal("skipping snapshot at %X/%08X while building logical decoding snapshot, xmin horizon too low",
1331 : : LSN_FORMAT_ARGS(lsn)),
1332 : : errdetail_internal("initial xmin horizon of %u vs the snapshot's %u",
1333 : : builder->initial_xmin_horizon, running->oldestRunningXid));
1334 : :
1335 : :
3279 andres@anarazel.de 1336 : 0 : SnapBuildWaitSnapshot(running, builder->initial_xmin_horizon);
1337 : :
4446 rhaas@postgresql.org 1338 : 0 : return true;
1339 : : }
1340 : :
1341 : : /*
1342 : : * a) No transaction were running, we can jump to consistent.
1343 : : *
1344 : : * This is not affected by races around xl_running_xacts, because we can
1345 : : * miss transaction commits, but currently not transactions starting.
1346 : : *
1347 : : * NB: We might have already started to incrementally assemble a snapshot,
1348 : : * so we need to be careful to deal with that.
1349 : : */
3279 andres@anarazel.de 1350 [ + + ]:CBC 1166 : if (running->oldestRunningXid == running->nextXid)
1351 : : {
180 alvherre@kurilemu.de 1352 [ + + ]:GNC 1132 : if (!XLogRecPtrIsValid(builder->start_decoding_at) ||
4352 andres@anarazel.de 1353 [ + + ]:CBC 639 : builder->start_decoding_at <= lsn)
1354 : : /* can decode everything after this */
1355 : 494 : builder->start_decoding_at = lsn + 1;
1356 : :
1357 : : /* As no transactions were running xmin/xmax can be trivially set. */
3240 tgl@sss.pgh.pa.us 1358 : 1132 : builder->xmin = running->nextXid; /* < are finished */
1359 : 1132 : builder->xmax = running->nextXid; /* >= are running */
1360 : :
1361 : : /* so we can safely use the faster comparisons */
4446 rhaas@postgresql.org 1362 [ - + ]: 1132 : Assert(TransactionIdIsNormal(builder->xmin));
1363 [ - + ]: 1132 : Assert(TransactionIdIsNormal(builder->xmax));
1364 : :
1365 : 1132 : builder->state = SNAPBUILD_CONSISTENT;
1905 andres@anarazel.de 1366 : 1132 : builder->next_phase_at = InvalidTransactionId;
1367 : :
25 fujii@postgresql.org 1368 [ + + + + ]:GNC 1132 : ereport(LogicalDecodingLogLevel(),
1369 : : errmsg("logical decoding found consistent point at %X/%08X",
1370 : : LSN_FORMAT_ARGS(lsn)),
1371 : : errdetail("There are no running transactions."));
1372 : :
4446 rhaas@postgresql.org 1373 :CBC 1132 : return false;
1374 : : }
1375 : :
1376 : : /*
1377 : : * b) valid on disk state and while neither building full snapshot nor
1378 : : * creating a slot.
1379 : : */
3295 andres@anarazel.de 1380 [ + + ]: 34 : else if (!builder->building_full_snapshot &&
663 msawada@postgresql.o 1381 [ + + + + ]: 52 : !builder->in_slot_creation &&
3295 andres@anarazel.de 1382 : 20 : SnapBuildRestore(builder, lsn))
1383 : : {
1384 : : /* there won't be any state to cleanup */
4446 rhaas@postgresql.org 1385 : 9 : return false;
1386 : : }
1387 : :
1388 : : /*
1389 : : * c) transition from START to BUILDING_SNAPSHOT.
1390 : : *
1391 : : * In START state, and a xl_running_xacts record with running xacts is
1392 : : * encountered. In that case, switch to BUILDING_SNAPSHOT state, and
1393 : : * record xl_running_xacts->nextXid. Once all running xacts have finished
1394 : : * (i.e. they're all >= nextXid), we have a complete catalog snapshot. It
1395 : : * might look that we could use xl_running_xacts's ->xids information to
1396 : : * get there quicker, but that is problematic because transactions marked
1397 : : * as running, might already have inserted their commit record - it's
1398 : : * infeasible to change that with locking.
1399 : : */
3279 andres@anarazel.de 1400 [ + + ]: 25 : else if (builder->state == SNAPBUILD_START)
1401 : : {
1402 : 14 : builder->state = SNAPBUILD_BUILDING_SNAPSHOT;
1905 1403 : 14 : builder->next_phase_at = running->nextXid;
1404 : :
1405 : : /*
1406 : : * Start with an xmin/xmax that's correct for future, when all the
1407 : : * currently running transactions have finished. We'll update both
1408 : : * while waiting for the pending transactions to finish.
1409 : : */
3240 tgl@sss.pgh.pa.us 1410 : 14 : builder->xmin = running->nextXid; /* < are finished */
1411 : 14 : builder->xmax = running->nextXid; /* >= are running */
1412 : :
1413 : : /* so we can safely use the faster comparisons */
4446 rhaas@postgresql.org 1414 [ - + ]: 14 : Assert(TransactionIdIsNormal(builder->xmin));
1415 [ - + ]: 14 : Assert(TransactionIdIsNormal(builder->xmax));
1416 : :
1417 [ + - ]: 14 : ereport(LOG,
1418 : : errmsg("logical decoding found initial starting point at %X/%08X",
1419 : : LSN_FORMAT_ARGS(lsn)),
1420 : : errdetail("Waiting for transactions (approximately %d) older than %u to end.",
1421 : : running->xcnt, running->nextXid));
1422 : :
3279 andres@anarazel.de 1423 : 14 : SnapBuildWaitSnapshot(running, running->nextXid);
1424 : : }
1425 : :
1426 : : /*
1427 : : * c) transition from BUILDING_SNAPSHOT to FULL_SNAPSHOT.
1428 : : *
1429 : : * In BUILDING_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid
1430 : : * is >= than nextXid from when we switched to BUILDING_SNAPSHOT. This
1431 : : * means all transactions starting afterwards have enough information to
1432 : : * be decoded. Switch to FULL_SNAPSHOT.
1433 : : */
1434 [ + + + + ]: 17 : else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
1905 1435 : 6 : TransactionIdPrecedesOrEquals(builder->next_phase_at,
1436 : : running->oldestRunningXid))
1437 : : {
3279 1438 : 5 : builder->state = SNAPBUILD_FULL_SNAPSHOT;
1905 1439 : 5 : builder->next_phase_at = running->nextXid;
1440 : :
3279 1441 [ + - ]: 5 : ereport(LOG,
1442 : : errmsg("logical decoding found initial consistent point at %X/%08X",
1443 : : LSN_FORMAT_ARGS(lsn)),
1444 : : errdetail("Waiting for transactions (approximately %d) older than %u to end.",
1445 : : running->xcnt, running->nextXid));
1446 : :
1447 : 5 : SnapBuildWaitSnapshot(running, running->nextXid);
1448 : : }
1449 : :
1450 : : /*
1451 : : * c) transition from FULL_SNAPSHOT to CONSISTENT.
1452 : : *
1453 : : * In FULL_SNAPSHOT state, and this xl_running_xacts' oldestRunningXid is
1454 : : * >= than nextXid from when we switched to FULL_SNAPSHOT. This means all
1455 : : * transactions that are currently in progress have a catalog snapshot,
1456 : : * and all their changes have been collected. Switch to CONSISTENT.
1457 : : */
1458 [ + + + - ]: 11 : else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
1905 1459 : 5 : TransactionIdPrecedesOrEquals(builder->next_phase_at,
1460 : : running->oldestRunningXid))
1461 : : {
3279 1462 : 5 : builder->state = SNAPBUILD_CONSISTENT;
1905 1463 : 5 : builder->next_phase_at = InvalidTransactionId;
1464 : :
25 fujii@postgresql.org 1465 [ + - - + ]:GNC 5 : ereport(LogicalDecodingLogLevel(),
1466 : : errmsg("logical decoding found consistent point at %X/%08X",
1467 : : LSN_FORMAT_ARGS(lsn)),
1468 : : errdetail("There are no old transactions anymore."));
1469 : : }
1470 : :
1471 : : /*
1472 : : * We already started to track running xacts and need to wait for all
1473 : : * in-progress ones to finish. We fall through to the normal processing of
1474 : : * records so incremental cleanup can be performed.
1475 : : */
4446 rhaas@postgresql.org 1476 :CBC 23 : return true;
1477 : : }
1478 : :
1479 : : /* ---
1480 : : * Iterate through xids in record, wait for all older than the cutoff to
1481 : : * finish. Then, if possible, log a new xl_running_xacts record.
1482 : : *
1483 : : * This isn't required for the correctness of decoding, but to:
1484 : : * a) allow isolationtester to notice that we're currently waiting for
1485 : : * something.
1486 : : * b) log a new xl_running_xacts record where it'd be helpful, without having
1487 : : * to wait for bgwriter or checkpointer.
1488 : : * ---
1489 : : */
1490 : : static void
3279 andres@anarazel.de 1491 : 19 : SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
1492 : : {
1493 : : int off;
1494 : :
1495 [ + + ]: 36 : for (off = 0; off < running->xcnt; off++)
1496 : : {
1497 : 19 : TransactionId xid = running->xids[off];
1498 : :
1499 : : /*
1500 : : * Upper layers should prevent that we ever need to wait on ourselves.
1501 : : * Check anyway, since failing to do so would either result in an
1502 : : * endless wait or an Assert() failure.
1503 : : */
1504 [ - + ]: 19 : if (TransactionIdIsCurrentTransactionId(xid))
3279 andres@anarazel.de 1505 [ # # ]:UBC 0 : elog(ERROR, "waiting for ourselves");
1506 : :
3279 andres@anarazel.de 1507 [ - + ]:CBC 19 : if (TransactionIdFollows(xid, cutoff))
3279 andres@anarazel.de 1508 :UBC 0 : continue;
1509 : :
3279 andres@anarazel.de 1510 :CBC 19 : XactLockTableWait(xid, NULL, NULL, XLTW_None);
1511 : : }
1512 : :
1513 : : /*
1514 : : * All transactions we needed to finish finished - try to ensure there is
1515 : : * another xl_running_xacts record in a timely manner, without having to
1516 : : * wait for bgwriter or checkpointer to log one. During recovery we can't
1517 : : * enforce that, so we'll have to wait.
1518 : : */
1519 [ + - ]: 17 : if (!RecoveryInProgress())
1520 : : {
1521 : : /*
1522 : : * If the last transaction info was about specific database, so needs
1523 : : * to be the next one - at least until we're in the CONSISTENT state.
1524 : : */
28 alvherre@kurilemu.de 1525 :GNC 17 : LogStandbySnapshot(running->dbid);
1526 : : }
3279 andres@anarazel.de 1527 :CBC 17 : }
1528 : :
1529 : : #define SnapBuildOnDiskConstantSize \
1530 : : offsetof(SnapBuildOnDisk, builder)
1531 : : #define SnapBuildOnDiskNotChecksummedSize \
1532 : : offsetof(SnapBuildOnDisk, version)
1533 : :
1534 : : #define SNAPBUILD_MAGIC 0x51A1E001
1535 : : #define SNAPBUILD_VERSION 6
1536 : :
1537 : : /*
1538 : : * Store/Load a snapshot from disk, depending on the snapshot builder's state.
1539 : : *
1540 : : * Supposed to be used by external (i.e. not snapbuild.c) code that just read
1541 : : * a record that's a potential location for a serialized snapshot.
1542 : : */
1543 : : void
4446 rhaas@postgresql.org 1544 : 80 : SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn)
1545 : : {
1546 [ - + ]: 80 : if (builder->state < SNAPBUILD_CONSISTENT)
4446 rhaas@postgresql.org 1547 :UBC 0 : SnapBuildRestore(builder, lsn);
1548 : : else
4446 rhaas@postgresql.org 1549 :CBC 80 : SnapBuildSerialize(builder, lsn);
1550 : 80 : }
1551 : :
1552 : : /*
1553 : : * Serialize the snapshot 'builder' at the location 'lsn' if it hasn't already
1554 : : * been done by another decoding process.
1555 : : */
1556 : : static void
1557 : 564 : SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
1558 : : {
1559 : : Size needed_length;
1938 akapila@postgresql.o 1560 : 564 : SnapBuildOnDisk *ondisk = NULL;
1363 1561 : 564 : TransactionId *catchange_xip = NULL;
1562 : : MemoryContext old_ctx;
1563 : : size_t catchange_xcnt;
1564 : : char *ondisk_c;
1565 : : int fd;
1566 : : char tmppath[MAXPGPATH];
1567 : : char path[MAXPGPATH];
1568 : : int ret;
1569 : : struct stat stat_buf;
1570 : : Size sz;
1571 : :
180 alvherre@kurilemu.de 1572 [ - + ]:GNC 564 : Assert(XLogRecPtrIsValid(lsn));
1573 [ + + - + ]: 564 : Assert(!XLogRecPtrIsValid(builder->last_serialized_snapshot) ||
1574 : : builder->last_serialized_snapshot <= lsn);
1575 : :
1576 : : /*
1577 : : * no point in serializing if we cannot continue to work immediately after
1578 : : * restoring the snapshot
1579 : : */
4446 rhaas@postgresql.org 1580 [ - + ]:CBC 564 : if (builder->state < SNAPBUILD_CONSISTENT)
4446 rhaas@postgresql.org 1581 :UBC 0 : return;
1582 : :
1583 : : /* consistent snapshots have no next phase */
1905 andres@anarazel.de 1584 [ - + ]:CBC 564 : Assert(builder->next_phase_at == InvalidTransactionId);
1585 : :
1586 : : /*
1587 : : * We identify snapshots by the LSN they are valid for. We don't need to
1588 : : * include timelines in the name as each LSN maps to exactly one timeline
1589 : : * unless the user used pg_resetwal or similar. If a user did so, there's
1590 : : * no hope continuing to decode anyway.
1591 : : */
613 michael@paquier.xyz 1592 : 564 : sprintf(path, "%s/%X-%X.snap",
1593 : : PG_LOGICAL_SNAPSHOTS_DIR,
1897 peter@eisentraut.org 1594 : 564 : LSN_FORMAT_ARGS(lsn));
1595 : :
1596 : : /*
1597 : : * first check whether some other backend already has written the snapshot
1598 : : * for this LSN. It's perfectly fine if there's none, so we accept ENOENT
1599 : : * as a valid state. Everything else is an unexpected error.
1600 : : */
4446 rhaas@postgresql.org 1601 : 564 : ret = stat(path, &stat_buf);
1602 : :
1603 [ + + - + ]: 564 : if (ret != 0 && errno != ENOENT)
4446 rhaas@postgresql.org 1604 [ # # ]:UBC 0 : ereport(ERROR,
1605 : : (errcode_for_file_access(),
1606 : : errmsg("could not stat file \"%s\": %m", path)));
1607 : :
4446 rhaas@postgresql.org 1608 [ + + ]:CBC 564 : else if (ret == 0)
1609 : : {
1610 : : /*
1611 : : * somebody else has already serialized to this point, don't overwrite
1612 : : * but remember location, so we don't need to read old data again.
1613 : : *
1614 : : * To be sure it has been synced to disk after the rename() from the
1615 : : * tempfile filename to the real filename, we just repeat the fsync.
1616 : : * That ought to be cheap because in most scenarios it should already
1617 : : * be safely on disk.
1618 : : */
1619 : 244 : fsync_fname(path, false);
613 michael@paquier.xyz 1620 : 244 : fsync_fname(PG_LOGICAL_SNAPSHOTS_DIR, true);
1621 : :
4446 rhaas@postgresql.org 1622 : 244 : builder->last_serialized_snapshot = lsn;
1623 : 244 : goto out;
1624 : : }
1625 : :
1626 : : /*
1627 : : * there is an obvious race condition here between the time we stat(2) the
1628 : : * file and us writing the file. But we rename the file into place
1629 : : * atomically and all files created need to contain the same data anyway,
1630 : : * so this is perfectly fine, although a bit of a resource waste. Locking
1631 : : * seems like pointless complication.
1632 : : */
1633 [ + + ]: 320 : elog(DEBUG1, "serializing snapshot to %s", path);
1634 : :
1635 : : /* to make sure only we will write to this tempfile, include pid */
613 michael@paquier.xyz 1636 : 320 : sprintf(tmppath, "%s/%X-%X.snap.%d.tmp",
1637 : : PG_LOGICAL_SNAPSHOTS_DIR,
1897 peter@eisentraut.org 1638 : 320 : LSN_FORMAT_ARGS(lsn), MyProcPid);
1639 : :
1640 : : /*
1641 : : * Unlink temporary file if it already exists, needs to have been before a
1642 : : * crash/error since we won't enter this function twice from within a
1643 : : * single decoding slot/backend and the temporary file contains the pid of
1644 : : * the current process.
1645 : : */
4446 rhaas@postgresql.org 1646 [ + - - + ]: 320 : if (unlink(tmppath) != 0 && errno != ENOENT)
4446 rhaas@postgresql.org 1647 [ # # ]:UBC 0 : ereport(ERROR,
1648 : : (errcode_for_file_access(),
1649 : : errmsg("could not remove file \"%s\": %m", tmppath)));
1650 : :
1363 akapila@postgresql.o 1651 :CBC 320 : old_ctx = MemoryContextSwitchTo(builder->context);
1652 : :
1653 : : /* Get the catalog modifying transactions that are yet not committed */
1654 : 320 : catchange_xip = ReorderBufferGetCatalogChangesXacts(builder->reorder);
1280 drowley@postgresql.o 1655 : 320 : catchange_xcnt = dclist_count(&builder->reorder->catchange_txns);
1656 : :
4446 rhaas@postgresql.org 1657 : 320 : needed_length = sizeof(SnapBuildOnDisk) +
1363 akapila@postgresql.o 1658 : 320 : sizeof(TransactionId) * (builder->committed.xcnt + catchange_xcnt);
1659 : :
1660 : 320 : ondisk_c = palloc0(needed_length);
4446 rhaas@postgresql.org 1661 : 320 : ondisk = (SnapBuildOnDisk *) ondisk_c;
1662 : 320 : ondisk->magic = SNAPBUILD_MAGIC;
1663 : 320 : ondisk->version = SNAPBUILD_VERSION;
1664 : 320 : ondisk->length = needed_length;
4200 heikki.linnakangas@i 1665 : 320 : INIT_CRC32C(ondisk->checksum);
1666 : 320 : COMP_CRC32C(ondisk->checksum,
1667 : : ((char *) ondisk) + SnapBuildOnDiskNotChecksummedSize,
1668 : : SnapBuildOnDiskConstantSize - SnapBuildOnDiskNotChecksummedSize);
4446 rhaas@postgresql.org 1669 : 320 : ondisk_c += sizeof(SnapBuildOnDisk);
1670 : :
1671 : 320 : memcpy(&ondisk->builder, builder, sizeof(SnapBuild));
1672 : : /* NULL-ify memory-only data */
1673 : 320 : ondisk->builder.context = NULL;
1674 : 320 : ondisk->builder.snapshot = NULL;
1675 : 320 : ondisk->builder.reorder = NULL;
1676 : 320 : ondisk->builder.committed.xip = NULL;
1363 akapila@postgresql.o 1677 : 320 : ondisk->builder.catchange.xip = NULL;
1678 : : /* update catchange only on disk data */
1679 : 320 : ondisk->builder.catchange.xcnt = catchange_xcnt;
1680 : :
4200 heikki.linnakangas@i 1681 : 320 : COMP_CRC32C(ondisk->checksum,
1682 : : &ondisk->builder,
1683 : : sizeof(SnapBuild));
1684 : :
1685 : : /* copy committed xacts */
1363 akapila@postgresql.o 1686 [ + + ]: 320 : if (builder->committed.xcnt > 0)
1687 : : {
1688 : 58 : sz = sizeof(TransactionId) * builder->committed.xcnt;
1689 : 58 : memcpy(ondisk_c, builder->committed.xip, sz);
1690 : 58 : COMP_CRC32C(ondisk->checksum, ondisk_c, sz);
1691 : 58 : ondisk_c += sz;
1692 : : }
1693 : :
1694 : : /* copy catalog modifying xacts */
1695 [ + + ]: 320 : if (catchange_xcnt > 0)
1696 : : {
1697 : 10 : sz = sizeof(TransactionId) * catchange_xcnt;
1698 : 10 : memcpy(ondisk_c, catchange_xip, sz);
1699 : 10 : COMP_CRC32C(ondisk->checksum, ondisk_c, sz);
1700 : 10 : ondisk_c += sz;
1701 : : }
1702 : :
4192 andres@anarazel.de 1703 : 320 : FIN_CRC32C(ondisk->checksum);
1704 : :
1705 : : /* we have valid data now, open tempfile and write it there */
4446 rhaas@postgresql.org 1706 : 320 : fd = OpenTransientFile(tmppath,
1707 : : O_CREAT | O_EXCL | O_WRONLY | PG_BINARY);
1708 [ - + ]: 320 : if (fd < 0)
4446 rhaas@postgresql.org 1709 [ # # ]:UBC 0 : ereport(ERROR,
1710 : : (errcode_for_file_access(),
1711 : : errmsg("could not open file \"%s\": %m", tmppath)));
1712 : :
2830 michael@paquier.xyz 1713 :CBC 320 : errno = 0;
3335 rhaas@postgresql.org 1714 : 320 : pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_WRITE);
4446 1715 [ - + ]: 320 : if ((write(fd, ondisk, needed_length)) != needed_length)
1716 : : {
2871 michael@paquier.xyz 1717 :UBC 0 : int save_errno = errno;
1718 : :
4446 rhaas@postgresql.org 1719 : 0 : CloseTransientFile(fd);
1720 : :
1721 : : /* if write didn't set errno, assume problem is no disk space */
2871 michael@paquier.xyz 1722 [ # # ]: 0 : errno = save_errno ? save_errno : ENOSPC;
4446 rhaas@postgresql.org 1723 [ # # ]: 0 : ereport(ERROR,
1724 : : (errcode_for_file_access(),
1725 : : errmsg("could not write to file \"%s\": %m", tmppath)));
1726 : : }
3335 rhaas@postgresql.org 1727 :CBC 320 : pgstat_report_wait_end();
1728 : :
1729 : : /*
1730 : : * fsync the file before renaming so that even if we crash after this we
1731 : : * have either a fully valid file or nothing.
1732 : : *
1733 : : * It's safe to just ERROR on fsync() here because we'll retry the whole
1734 : : * operation including the writes.
1735 : : *
1736 : : * TODO: Do the fsync() via checkpoints/restartpoints, doing it here has
1737 : : * some noticeable overhead since it's performed synchronously during
1738 : : * decoding?
1739 : : */
1740 : 320 : pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_SYNC);
4446 1741 [ - + ]: 320 : if (pg_fsync(fd) != 0)
1742 : : {
2871 michael@paquier.xyz 1743 :UBC 0 : int save_errno = errno;
1744 : :
4446 rhaas@postgresql.org 1745 : 0 : CloseTransientFile(fd);
2871 michael@paquier.xyz 1746 : 0 : errno = save_errno;
4446 rhaas@postgresql.org 1747 [ # # ]: 0 : ereport(ERROR,
1748 : : (errcode_for_file_access(),
1749 : : errmsg("could not fsync file \"%s\": %m", tmppath)));
1750 : : }
3335 rhaas@postgresql.org 1751 :CBC 320 : pgstat_report_wait_end();
1752 : :
2495 peter@eisentraut.org 1753 [ - + ]: 320 : if (CloseTransientFile(fd) != 0)
2614 michael@paquier.xyz 1754 [ # # ]:UBC 0 : ereport(ERROR,
1755 : : (errcode_for_file_access(),
1756 : : errmsg("could not close file \"%s\": %m", tmppath)));
1757 : :
613 michael@paquier.xyz 1758 :CBC 320 : fsync_fname(PG_LOGICAL_SNAPSHOTS_DIR, true);
1759 : :
1760 : : /*
1761 : : * We may overwrite the work from some other backend, but that's ok, our
1762 : : * snapshot is valid as well, we'll just have done some superfluous work.
1763 : : */
4446 rhaas@postgresql.org 1764 [ - + ]: 320 : if (rename(tmppath, path) != 0)
1765 : : {
4446 rhaas@postgresql.org 1766 [ # # ]:UBC 0 : ereport(ERROR,
1767 : : (errcode_for_file_access(),
1768 : : errmsg("could not rename file \"%s\" to \"%s\": %m",
1769 : : tmppath, path)));
1770 : : }
1771 : :
1772 : : /* make sure we persist */
4446 rhaas@postgresql.org 1773 :CBC 320 : fsync_fname(path, false);
613 michael@paquier.xyz 1774 : 320 : fsync_fname(PG_LOGICAL_SNAPSHOTS_DIR, true);
1775 : :
1776 : : /*
1777 : : * Now there's no way we can lose the dumped state anymore, remember this
1778 : : * as a serialization point.
1779 : : */
4446 rhaas@postgresql.org 1780 : 320 : builder->last_serialized_snapshot = lsn;
1781 : :
1363 akapila@postgresql.o 1782 : 320 : MemoryContextSwitchTo(old_ctx);
1783 : :
4446 rhaas@postgresql.org 1784 : 564 : out:
1785 : 564 : ReorderBufferSetRestartPoint(builder->reorder,
1786 : : builder->last_serialized_snapshot);
1787 : : /* be tidy */
1938 akapila@postgresql.o 1788 [ + + ]: 564 : if (ondisk)
1789 : 320 : pfree(ondisk);
1363 1790 [ + + ]: 564 : if (catchange_xip)
1791 : 10 : pfree(catchange_xip);
1792 : : }
1793 : :
1794 : : /*
1795 : : * Restore the logical snapshot file contents to 'ondisk'.
1796 : : *
1797 : : * 'context' is the memory context where the catalog modifying/committed xid
1798 : : * will live.
1799 : : * If 'missing_ok' is true, will not throw an error if the file is not found.
1800 : : */
1801 : : bool
420 msawada@postgresql.o 1802 : 22 : SnapBuildRestoreSnapshot(SnapBuildOnDisk *ondisk, XLogRecPtr lsn,
1803 : : MemoryContext context, bool missing_ok)
1804 : : {
1805 : : int fd;
1806 : : pg_crc32c checksum;
1807 : : Size sz;
1808 : : char path[MAXPGPATH];
1809 : :
1810 : 22 : sprintf(path, "%s/%X-%X.snap",
1811 : : PG_LOGICAL_SNAPSHOTS_DIR,
1812 : 22 : LSN_FORMAT_ARGS(lsn));
1813 : :
3146 peter_e@gmx.net 1814 : 22 : fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
1815 : :
568 msawada@postgresql.o 1816 [ + + ]: 22 : if (fd < 0)
1817 : : {
1818 [ + - + - ]: 11 : if (missing_ok && errno == ENOENT)
1819 : 11 : return false;
1820 : :
4446 rhaas@postgresql.org 1821 [ # # ]:UBC 0 : ereport(ERROR,
1822 : : (errcode_for_file_access(),
1823 : : errmsg("could not open file \"%s\": %m", path)));
1824 : : }
1825 : :
1826 : : /* ----
1827 : : * Make sure the snapshot had been stored safely to disk, that's normally
1828 : : * cheap.
1829 : : * Note that we do not need PANIC here, nobody will be able to use the
1830 : : * slot without fsyncing, and saving it won't succeed without an fsync()
1831 : : * either...
1832 : : * ----
1833 : : */
4446 rhaas@postgresql.org 1834 :CBC 11 : fsync_fname(path, false);
613 michael@paquier.xyz 1835 : 11 : fsync_fname(PG_LOGICAL_SNAPSHOTS_DIR, true);
1836 : :
1837 : : /* read statically sized portion of snapshot */
588 peter@eisentraut.org 1838 : 11 : SnapBuildRestoreContents(fd, ondisk, SnapBuildOnDiskConstantSize, path);
1839 : :
568 msawada@postgresql.o 1840 [ - + ]: 11 : if (ondisk->magic != SNAPBUILD_MAGIC)
4446 rhaas@postgresql.org 1841 [ # # ]:UBC 0 : ereport(ERROR,
1842 : : (errcode(ERRCODE_DATA_CORRUPTED),
1843 : : errmsg("snapbuild state file \"%s\" has wrong magic number: %u instead of %u",
1844 : : path, ondisk->magic, SNAPBUILD_MAGIC)));
1845 : :
568 msawada@postgresql.o 1846 [ - + ]:CBC 11 : if (ondisk->version != SNAPBUILD_VERSION)
4446 rhaas@postgresql.org 1847 [ # # ]:UBC 0 : ereport(ERROR,
1848 : : (errcode(ERRCODE_DATA_CORRUPTED),
1849 : : errmsg("snapbuild state file \"%s\" has unsupported version: %u instead of %u",
1850 : : path, ondisk->version, SNAPBUILD_VERSION)));
1851 : :
4200 heikki.linnakangas@i 1852 :CBC 11 : INIT_CRC32C(checksum);
1853 : 11 : COMP_CRC32C(checksum,
1854 : : ((char *) ondisk) + SnapBuildOnDiskNotChecksummedSize,
1855 : : SnapBuildOnDiskConstantSize - SnapBuildOnDiskNotChecksummedSize);
1856 : :
1857 : : /* read SnapBuild */
588 peter@eisentraut.org 1858 : 11 : SnapBuildRestoreContents(fd, &ondisk->builder, sizeof(SnapBuild), path);
568 msawada@postgresql.o 1859 : 11 : COMP_CRC32C(checksum, &ondisk->builder, sizeof(SnapBuild));
1860 : :
1861 : : /* restore committed xacts information */
1862 [ + + ]: 11 : if (ondisk->builder.committed.xcnt > 0)
1863 : : {
1864 : 5 : sz = sizeof(TransactionId) * ondisk->builder.committed.xcnt;
1865 : 5 : ondisk->builder.committed.xip = MemoryContextAllocZero(context, sz);
588 peter@eisentraut.org 1866 : 5 : SnapBuildRestoreContents(fd, ondisk->builder.committed.xip, sz, path);
568 msawada@postgresql.o 1867 : 5 : COMP_CRC32C(checksum, ondisk->builder.committed.xip, sz);
1868 : : }
1869 : :
1870 : : /* restore catalog modifying xacts information */
1871 [ + + ]: 11 : if (ondisk->builder.catchange.xcnt > 0)
1872 : : {
1873 : 5 : sz = sizeof(TransactionId) * ondisk->builder.catchange.xcnt;
1874 : 5 : ondisk->builder.catchange.xip = MemoryContextAllocZero(context, sz);
588 peter@eisentraut.org 1875 : 5 : SnapBuildRestoreContents(fd, ondisk->builder.catchange.xip, sz, path);
568 msawada@postgresql.o 1876 : 5 : COMP_CRC32C(checksum, ondisk->builder.catchange.xip, sz);
1877 : : }
1878 : :
2495 peter@eisentraut.org 1879 [ - + ]: 11 : if (CloseTransientFile(fd) != 0)
2614 michael@paquier.xyz 1880 [ # # ]:UBC 0 : ereport(ERROR,
1881 : : (errcode_for_file_access(),
1882 : : errmsg("could not close file \"%s\": %m", path)));
1883 : :
4192 andres@anarazel.de 1884 :CBC 11 : FIN_CRC32C(checksum);
1885 : :
1886 : : /* verify checksum of what we've read */
568 msawada@postgresql.o 1887 [ - + ]: 11 : if (!EQ_CRC32C(checksum, ondisk->checksum))
4446 rhaas@postgresql.org 1888 [ # # ]:UBC 0 : ereport(ERROR,
1889 : : (errcode(ERRCODE_DATA_CORRUPTED),
1890 : : errmsg("checksum mismatch for snapbuild state file \"%s\": is %u, should be %u",
1891 : : path, checksum, ondisk->checksum)));
1892 : :
568 msawada@postgresql.o 1893 :CBC 11 : return true;
1894 : : }
1895 : :
1896 : : /*
1897 : : * Restore a snapshot into 'builder' if previously one has been stored at the
1898 : : * location indicated by 'lsn'. Returns true if successful, false otherwise.
1899 : : */
1900 : : static bool
1901 : 20 : SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
1902 : : {
1903 : : SnapBuildOnDisk ondisk;
1904 : :
1905 : : /* no point in loading a snapshot if we're already there */
1906 [ - + ]: 20 : if (builder->state == SNAPBUILD_CONSISTENT)
568 msawada@postgresql.o 1907 :UBC 0 : return false;
1908 : :
1909 : : /* validate and restore the snapshot to 'ondisk' */
420 msawada@postgresql.o 1910 [ + + ]:CBC 20 : if (!SnapBuildRestoreSnapshot(&ondisk, lsn, builder->context, true))
568 1911 : 11 : return false;
1912 : :
1913 : : /*
1914 : : * ok, we now have a sensible snapshot here, figure out if it has more
1915 : : * information than we have.
1916 : : */
1917 : :
1918 : : /*
1919 : : * We are only interested in consistent snapshots for now, comparing
1920 : : * whether one incomplete snapshot is more "advanced" seems to be
1921 : : * unnecessarily complex.
1922 : : */
4446 rhaas@postgresql.org 1923 [ - + ]: 9 : if (ondisk.builder.state < SNAPBUILD_CONSISTENT)
4446 rhaas@postgresql.org 1924 :UBC 0 : goto snapshot_not_interesting;
1925 : :
1926 : : /*
1927 : : * Don't use a snapshot that requires an xmin that we cannot guarantee to
1928 : : * be available.
1929 : : */
4446 rhaas@postgresql.org 1930 [ - + ]:CBC 9 : if (TransactionIdPrecedes(ondisk.builder.xmin, builder->initial_xmin_horizon))
4446 rhaas@postgresql.org 1931 :UBC 0 : goto snapshot_not_interesting;
1932 : :
1933 : : /*
1934 : : * Consistent snapshots have no next phase. Reset next_phase_at as it is
1935 : : * possible that an old value may remain.
1936 : : */
1905 andres@anarazel.de 1937 [ - + ]:CBC 9 : Assert(ondisk.builder.next_phase_at == InvalidTransactionId);
1036 dgustafsson@postgres 1938 : 9 : builder->next_phase_at = InvalidTransactionId;
1939 : :
1940 : : /* ok, we think the snapshot is sensible, copy over everything important */
4446 rhaas@postgresql.org 1941 : 9 : builder->xmin = ondisk.builder.xmin;
1942 : 9 : builder->xmax = ondisk.builder.xmax;
1943 : 9 : builder->state = ondisk.builder.state;
1944 : :
1945 : 9 : builder->committed.xcnt = ondisk.builder.committed.xcnt;
1946 : : /* We only allocated/stored xcnt, not xcnt_space xids ! */
1947 : : /* don't overwrite preallocated xip, if we don't have anything here */
1948 [ + + ]: 9 : if (builder->committed.xcnt > 0)
1949 : : {
1950 : 3 : pfree(builder->committed.xip);
1951 : 3 : builder->committed.xcnt_space = ondisk.builder.committed.xcnt;
1952 : 3 : builder->committed.xip = ondisk.builder.committed.xip;
1953 : : }
1954 : 9 : ondisk.builder.committed.xip = NULL;
1955 : :
1956 : : /* set catalog modifying transactions */
1363 akapila@postgresql.o 1957 [ - + ]: 9 : if (builder->catchange.xip)
1363 akapila@postgresql.o 1958 :UBC 0 : pfree(builder->catchange.xip);
1363 akapila@postgresql.o 1959 :CBC 9 : builder->catchange.xcnt = ondisk.builder.catchange.xcnt;
1960 : 9 : builder->catchange.xip = ondisk.builder.catchange.xip;
1961 : 9 : ondisk.builder.catchange.xip = NULL;
1962 : :
1963 : : /* our snapshot is not interesting anymore, build a new one */
4446 rhaas@postgresql.org 1964 [ - + ]: 9 : if (builder->snapshot != NULL)
1965 : : {
4446 rhaas@postgresql.org 1966 :UBC 0 : SnapBuildSnapDecRefcount(builder->snapshot);
1967 : : }
3247 andres@anarazel.de 1968 :CBC 9 : builder->snapshot = SnapBuildBuildSnapshot(builder);
4446 rhaas@postgresql.org 1969 : 9 : SnapBuildSnapIncRefcount(builder->snapshot);
1970 : :
1971 : 9 : ReorderBufferSetRestartPoint(builder->reorder, lsn);
1972 : :
1973 [ - + ]: 9 : Assert(builder->state == SNAPBUILD_CONSISTENT);
1974 : :
25 fujii@postgresql.org 1975 [ + + + + ]:GNC 9 : ereport(LogicalDecodingLogLevel(),
1976 : : errmsg("logical decoding found consistent point at %X/%08X",
1977 : : LSN_FORMAT_ARGS(lsn)),
1978 : : errdetail("Logical decoding will begin using saved snapshot."));
4446 rhaas@postgresql.org 1979 :CBC 9 : return true;
1980 : :
4446 rhaas@postgresql.org 1981 :UBC 0 : snapshot_not_interesting:
1982 [ # # ]: 0 : if (ondisk.builder.committed.xip != NULL)
1983 : 0 : pfree(ondisk.builder.committed.xip);
1363 akapila@postgresql.o 1984 [ # # ]: 0 : if (ondisk.builder.catchange.xip != NULL)
1985 : 0 : pfree(ondisk.builder.catchange.xip);
4446 rhaas@postgresql.org 1986 : 0 : return false;
1987 : : }
1988 : :
1989 : : /*
1990 : : * Read the contents of the serialized snapshot to 'dest'.
1991 : : */
1992 : : static void
588 peter@eisentraut.org 1993 :CBC 32 : SnapBuildRestoreContents(int fd, void *dest, Size size, const char *path)
1994 : : {
1995 : : int readBytes;
1996 : :
1363 akapila@postgresql.o 1997 : 32 : pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
1998 : 32 : readBytes = read(fd, dest, size);
1999 : 32 : pgstat_report_wait_end();
2000 [ - + ]: 32 : if (readBytes != size)
2001 : : {
1363 akapila@postgresql.o 2002 :UBC 0 : int save_errno = errno;
2003 : :
2004 : 0 : CloseTransientFile(fd);
2005 : :
2006 [ # # ]: 0 : if (readBytes < 0)
2007 : : {
2008 : 0 : errno = save_errno;
2009 [ # # ]: 0 : ereport(ERROR,
2010 : : (errcode_for_file_access(),
2011 : : errmsg("could not read file \"%s\": %m", path)));
2012 : : }
2013 : : else
2014 [ # # ]: 0 : ereport(ERROR,
2015 : : (errcode(ERRCODE_DATA_CORRUPTED),
2016 : : errmsg("could not read file \"%s\": read %d of %zu",
2017 : : path, readBytes, size)));
2018 : : }
1363 akapila@postgresql.o 2019 :CBC 32 : }
2020 : :
2021 : : /*
2022 : : * Remove all serialized snapshots that are not required anymore because no
2023 : : * slot can need them. This doesn't actually have to run during a checkpoint,
2024 : : * but it's a convenient point to schedule this.
2025 : : *
2026 : : * NB: We run this during checkpoints even if logical decoding is disabled so
2027 : : * we cleanup old slots at some point after it got disabled.
2028 : : */
2029 : : void
4446 rhaas@postgresql.org 2030 : 1944 : CheckPointSnapBuild(void)
2031 : : {
2032 : : XLogRecPtr cutoff;
2033 : : XLogRecPtr redo;
2034 : : DIR *snap_dir;
2035 : : struct dirent *snap_de;
2036 : : char path[MAXPGPATH + sizeof(PG_LOGICAL_SNAPSHOTS_DIR)];
2037 : :
2038 : : /*
2039 : : * We start off with a minimum of the last redo pointer. No new
2040 : : * replication slot will start before that, so that's a safe upper bound
2041 : : * for removal.
2042 : : */
2043 : 1944 : redo = GetRedoRecPtr();
2044 : :
2045 : : /* now check for the restart ptrs from existing slots */
2046 : 1944 : cutoff = ReplicationSlotsComputeLogicalRestartLSN();
2047 : :
2048 : : /* don't start earlier than the restart lsn */
2049 [ + + ]: 1944 : if (redo < cutoff)
2050 : 1 : cutoff = redo;
2051 : :
613 michael@paquier.xyz 2052 : 1944 : snap_dir = AllocateDir(PG_LOGICAL_SNAPSHOTS_DIR);
2053 [ + + ]: 6131 : while ((snap_de = ReadDir(snap_dir, PG_LOGICAL_SNAPSHOTS_DIR)) != NULL)
2054 : : {
2055 : : uint32 hi;
2056 : : uint32 lo;
2057 : : XLogRecPtr lsn;
2058 : : PGFileType de_type;
2059 : :
4446 rhaas@postgresql.org 2060 [ + + ]: 4187 : if (strcmp(snap_de->d_name, ".") == 0 ||
2061 [ + + ]: 2243 : strcmp(snap_de->d_name, "..") == 0)
2062 : 3888 : continue;
2063 : :
613 michael@paquier.xyz 2064 : 299 : snprintf(path, sizeof(path), "%s/%s", PG_LOGICAL_SNAPSHOTS_DIR, snap_de->d_name);
1341 2065 : 299 : de_type = get_dirent_type(path, snap_de, false, DEBUG1);
2066 : :
2067 [ + - - + ]: 299 : if (de_type != PGFILETYPE_ERROR && de_type != PGFILETYPE_REG)
2068 : : {
4446 rhaas@postgresql.org 2069 [ # # ]:UBC 0 : elog(DEBUG1, "only regular files expected: %s", path);
2070 : 0 : continue;
2071 : : }
2072 : :
2073 : : /*
2074 : : * temporary filenames from SnapBuildSerialize() include the LSN and
2075 : : * everything but are postfixed by .$pid.tmp. We can just remove them
2076 : : * the same as other files because there can be none that are
2077 : : * currently being written that are older than cutoff.
2078 : : *
2079 : : * We just log a message if a file doesn't fit the pattern, it's
2080 : : * probably some editors lock/state file or similar...
2081 : : */
4446 rhaas@postgresql.org 2082 [ - + ]:CBC 299 : if (sscanf(snap_de->d_name, "%X-%X.snap", &hi, &lo) != 2)
2083 : : {
4446 rhaas@postgresql.org 2084 [ # # ]:UBC 0 : ereport(LOG,
2085 : : (errmsg("could not parse file name \"%s\"", path)));
2086 : 0 : continue;
2087 : : }
2088 : :
4446 rhaas@postgresql.org 2089 :CBC 299 : lsn = ((uint64) hi) << 32 | lo;
2090 : :
2091 : : /* check whether we still need it */
180 alvherre@kurilemu.de 2092 [ + + + + ]:GNC 299 : if (lsn < cutoff || !XLogRecPtrIsValid(cutoff))
2093 : : {
4446 rhaas@postgresql.org 2094 [ + + ]:CBC 195 : elog(DEBUG1, "removing snapbuild snapshot %s", path);
2095 : :
2096 : : /*
2097 : : * It's not particularly harmful, though strange, if we can't
2098 : : * remove the file here. Don't prevent the checkpoint from
2099 : : * completing, that'd be a cure worse than the disease.
2100 : : */
2101 [ - + ]: 195 : if (unlink(path) < 0)
2102 : : {
4446 rhaas@postgresql.org 2103 [ # # ]:UBC 0 : ereport(LOG,
2104 : : (errcode_for_file_access(),
2105 : : errmsg("could not remove file \"%s\": %m",
2106 : : path)));
2107 : 0 : continue;
2108 : : }
2109 : : }
2110 : : }
4446 rhaas@postgresql.org 2111 :CBC 1944 : FreeDir(snap_dir);
2112 : 1944 : }
2113 : :
2114 : : /*
2115 : : * Check if a logical snapshot at the specified point has been serialized.
2116 : : */
2117 : : bool
762 akapila@postgresql.o 2118 : 13 : SnapBuildSnapshotExists(XLogRecPtr lsn)
2119 : : {
2120 : : char path[MAXPGPATH];
2121 : : int ret;
2122 : : struct stat stat_buf;
2123 : :
264 fujii@postgresql.org 2124 : 13 : sprintf(path, "%s/%X-%X.snap",
2125 : : PG_LOGICAL_SNAPSHOTS_DIR,
762 akapila@postgresql.o 2126 : 13 : LSN_FORMAT_ARGS(lsn));
2127 : :
2128 : 13 : ret = stat(path, &stat_buf);
2129 : :
2130 [ + + - + ]: 13 : if (ret != 0 && errno != ENOENT)
762 akapila@postgresql.o 2131 [ # # ]:UBC 0 : ereport(ERROR,
2132 : : (errcode_for_file_access(),
2133 : : errmsg("could not stat file \"%s\": %m", path)));
2134 : :
762 akapila@postgresql.o 2135 :CBC 13 : return ret == 0;
2136 : : }
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