Age Owner Branch data TLA Line data Source code
1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * clog.c
4 : : * PostgreSQL transaction-commit-log manager
5 : : *
6 : : * This module stores two bits per transaction regarding its commit/abort
7 : : * status; the status for four transactions fit in a byte.
8 : : *
9 : : * This would be a pretty simple abstraction on top of slru.c, except that
10 : : * for performance reasons we allow multiple transactions that are
11 : : * committing concurrently to form a queue, so that a single process can
12 : : * update the status for all of them within a single lock acquisition run.
13 : : *
14 : : * XLOG interactions: this module generates an XLOG record whenever a new
15 : : * CLOG page is initialized to zeroes. Other writes of CLOG come from
16 : : * recording of transaction commit or abort in xact.c, which generates its
17 : : * own XLOG records for these events and will re-perform the status update
18 : : * on redo; so we need make no additional XLOG entry here. For synchronous
19 : : * transaction commits, the XLOG is guaranteed flushed through the XLOG commit
20 : : * record before we are called to log a commit, so the WAL rule "write xlog
21 : : * before data" is satisfied automatically. However, for async commits we
22 : : * must track the latest LSN affecting each CLOG page, so that we can flush
23 : : * XLOG that far and satisfy the WAL rule. We don't have to worry about this
24 : : * for aborts (whether sync or async), since the post-crash assumption would
25 : : * be that such transactions failed anyway.
26 : : *
27 : : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
28 : : * Portions Copyright (c) 1994, Regents of the University of California
29 : : *
30 : : * src/backend/access/transam/clog.c
31 : : *
32 : : *-------------------------------------------------------------------------
33 : : */
34 : : #include "postgres.h"
35 : :
36 : : #include "access/clog.h"
37 : : #include "access/slru.h"
38 : : #include "access/transam.h"
39 : : #include "access/xlog.h"
40 : : #include "access/xloginsert.h"
41 : : #include "access/xlogutils.h"
42 : : #include "miscadmin.h"
43 : : #include "pg_trace.h"
44 : : #include "pgstat.h"
45 : : #include "storage/proc.h"
46 : : #include "storage/sync.h"
47 : : #include "utils/guc_hooks.h"
48 : :
49 : : /*
50 : : * Defines for CLOG page sizes. A page is the same BLCKSZ as is used
51 : : * everywhere else in Postgres.
52 : : *
53 : : * Note: because TransactionIds are 32 bits and wrap around at 0xFFFFFFFF,
54 : : * CLOG page numbering also wraps around at 0xFFFFFFFF/CLOG_XACTS_PER_PAGE,
55 : : * and CLOG segment numbering at
56 : : * 0xFFFFFFFF/CLOG_XACTS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need take no
57 : : * explicit notice of that fact in this module, except when comparing segment
58 : : * and page numbers in TruncateCLOG (see CLOGPagePrecedes).
59 : : */
60 : :
61 : : /* We need two bits per xact, so four xacts fit in a byte */
62 : : #define CLOG_BITS_PER_XACT 2
63 : : #define CLOG_XACTS_PER_BYTE 4
64 : : #define CLOG_XACTS_PER_PAGE (BLCKSZ * CLOG_XACTS_PER_BYTE)
65 : : #define CLOG_XACT_BITMASK ((1 << CLOG_BITS_PER_XACT) - 1)
66 : :
67 : : /*
68 : : * Because space used in CLOG by each transaction is so small, we place a
69 : : * smaller limit on the number of CLOG buffers than SLRU allows. No other
70 : : * SLRU needs this.
71 : : */
72 : : #define CLOG_MAX_ALLOWED_BUFFERS \
73 : : Min(SLRU_MAX_ALLOWED_BUFFERS, \
74 : : (((MaxTransactionId / 2) + (CLOG_XACTS_PER_PAGE - 1)) / CLOG_XACTS_PER_PAGE))
75 : :
76 : :
77 : : /*
78 : : * Although we return an int64 the actual value can't currently exceed
79 : : * 0xFFFFFFFF/CLOG_XACTS_PER_PAGE.
80 : : */
81 : : static inline int64
647 akorotkov@postgresql 82 :CBC 1029825 : TransactionIdToPage(TransactionId xid)
83 : : {
84 : 1029825 : return xid / (int64) CLOG_XACTS_PER_PAGE;
85 : : }
86 : :
87 : : #define TransactionIdToPgIndex(xid) ((xid) % (TransactionId) CLOG_XACTS_PER_PAGE)
88 : : #define TransactionIdToByte(xid) (TransactionIdToPgIndex(xid) / CLOG_XACTS_PER_BYTE)
89 : : #define TransactionIdToBIndex(xid) ((xid) % (TransactionId) CLOG_XACTS_PER_BYTE)
90 : :
91 : : /* We store the latest async LSN for each group of transactions */
92 : : #define CLOG_XACTS_PER_LSN_GROUP 32 /* keep this a power of 2 */
93 : : #define CLOG_LSNS_PER_PAGE (CLOG_XACTS_PER_PAGE / CLOG_XACTS_PER_LSN_GROUP)
94 : :
95 : : #define GetLSNIndex(slotno, xid) ((slotno) * CLOG_LSNS_PER_PAGE + \
96 : : ((xid) % (TransactionId) CLOG_XACTS_PER_PAGE) / CLOG_XACTS_PER_LSN_GROUP)
97 : :
98 : : /*
99 : : * The number of subtransactions below which we consider to apply clog group
100 : : * update optimization. Testing reveals that the number higher than this can
101 : : * hurt performance.
102 : : */
103 : : #define THRESHOLD_SUBTRANS_CLOG_OPT 5
104 : :
105 : : /*
106 : : * Link to shared-memory data structures for CLOG control
107 : : */
108 : : static SlruCtlData XactCtlData;
109 : :
110 : : #define XactCtl (&XactCtlData)
111 : :
112 : :
113 : : static bool CLOGPagePrecedes(int64 page1, int64 page2);
114 : : static void WriteTruncateXlogRec(int64 pageno, TransactionId oldestXact,
115 : : Oid oldestXactDb);
116 : : static void TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
117 : : TransactionId *subxids, XidStatus status,
118 : : XLogRecPtr lsn, int64 pageno,
119 : : bool all_xact_same_page);
120 : : static void TransactionIdSetStatusBit(TransactionId xid, XidStatus status,
121 : : XLogRecPtr lsn, int slotno);
122 : : static void set_status_by_pages(int nsubxids, TransactionId *subxids,
123 : : XidStatus status, XLogRecPtr lsn);
124 : : static bool TransactionGroupUpdateXidStatus(TransactionId xid,
125 : : XidStatus status, XLogRecPtr lsn, int64 pageno);
126 : : static void TransactionIdSetPageStatusInternal(TransactionId xid, int nsubxids,
127 : : TransactionId *subxids, XidStatus status,
128 : : XLogRecPtr lsn, int64 pageno);
129 : :
130 : :
131 : : /*
132 : : * TransactionIdSetTreeStatus
133 : : *
134 : : * Record the final state of transaction entries in the commit log for
135 : : * a transaction and its subtransaction tree. Take care to ensure this is
136 : : * efficient, and as atomic as possible.
137 : : *
138 : : * xid is a single xid to set status for. This will typically be
139 : : * the top level transactionid for a top level commit or abort. It can
140 : : * also be a subtransaction when we record transaction aborts.
141 : : *
142 : : * subxids is an array of xids of length nsubxids, representing subtransactions
143 : : * in the tree of xid. In various cases nsubxids may be zero.
144 : : *
145 : : * lsn must be the WAL location of the commit record when recording an async
146 : : * commit. For a synchronous commit it can be InvalidXLogRecPtr, since the
147 : : * caller guarantees the commit record is already flushed in that case. It
148 : : * should be InvalidXLogRecPtr for abort cases, too.
149 : : *
150 : : * In the commit case, atomicity is limited by whether all the subxids are in
151 : : * the same CLOG page as xid. If they all are, then the lock will be grabbed
152 : : * only once, and the status will be set to committed directly. Otherwise
153 : : * we must
154 : : * 1. set sub-committed all subxids that are not on the same page as the
155 : : * main xid
156 : : * 2. atomically set committed the main xid and the subxids on the same page
157 : : * 3. go over the first bunch again and set them committed
158 : : * Note that as far as concurrent checkers are concerned, main transaction
159 : : * commit as a whole is still atomic.
160 : : *
161 : : * Example:
162 : : * TransactionId t commits and has subxids t1, t2, t3, t4
163 : : * t is on page p1, t1 is also on p1, t2 and t3 are on p2, t4 is on p3
164 : : * 1. update pages2-3:
165 : : * page2: set t2,t3 as sub-committed
166 : : * page3: set t4 as sub-committed
167 : : * 2. update page1:
168 : : * page1: set t,t1 as committed
169 : : * 3. update pages2-3:
170 : : * page2: set t2,t3 as committed
171 : : * page3: set t4 as committed
172 : : *
173 : : * NB: this is a low-level routine and is NOT the preferred entry point
174 : : * for most uses; functions in transam.c are the intended callers.
175 : : *
176 : : * XXX Think about issuing POSIX_FADV_WILLNEED on pages that we will need,
177 : : * but aren't yet in cache, as well as hinting pages not to fall out of
178 : : * cache yet.
179 : : */
180 : : void
6165 alvherre@alvh.no-ip. 181 : 152100 : TransactionIdSetTreeStatus(TransactionId xid, int nsubxids,
182 : : TransactionId *subxids, XidStatus status, XLogRecPtr lsn)
183 : : {
647 akorotkov@postgresql 184 : 152100 : int64 pageno = TransactionIdToPage(xid); /* get page of parent */
185 : : int i;
186 : :
6165 alvherre@alvh.no-ip. 187 [ + + - + ]: 152100 : Assert(status == TRANSACTION_STATUS_COMMITTED ||
188 : : status == TRANSACTION_STATUS_ABORTED);
189 : :
190 : : /*
191 : : * See how many subxids, if any, are on the same page as the parent, if
192 : : * any.
193 : : */
194 [ + + ]: 156204 : for (i = 0; i < nsubxids; i++)
195 : : {
196 [ - + ]: 4104 : if (TransactionIdToPage(subxids[i]) != pageno)
6165 alvherre@alvh.no-ip. 197 :UBC 0 : break;
198 : : }
199 : :
200 : : /*
201 : : * Do all items fit on a single page?
202 : : */
6165 alvherre@alvh.no-ip. 203 [ + - ]:CBC 152100 : if (i == nsubxids)
204 : : {
205 : : /*
206 : : * Set the parent and all subtransactions in a single call
207 : : */
208 : 152100 : TransactionIdSetPageStatus(xid, nsubxids, subxids, status, lsn,
209 : : pageno, true);
210 : : }
211 : : else
212 : : {
5931 bruce@momjian.us 213 :UBC 0 : int nsubxids_on_first_page = i;
214 : :
215 : : /*
216 : : * If this is a commit then we care about doing this correctly (i.e.
217 : : * using the subcommitted intermediate status). By here, we know
218 : : * we're updating more than one page of clog, so we must mark entries
219 : : * that are *not* on the first page so that they show as subcommitted
220 : : * before we then return to update the status to fully committed.
221 : : *
222 : : * To avoid touching the first page twice, skip marking subcommitted
223 : : * for the subxids on that first page.
224 : : */
6165 alvherre@alvh.no-ip. 225 [ # # ]: 0 : if (status == TRANSACTION_STATUS_COMMITTED)
226 : 0 : set_status_by_pages(nsubxids - nsubxids_on_first_page,
227 : 0 : subxids + nsubxids_on_first_page,
228 : : TRANSACTION_STATUS_SUB_COMMITTED, lsn);
229 : :
230 : : /*
231 : : * Now set the parent and subtransactions on same page as the parent,
232 : : * if any
233 : : */
234 : 0 : pageno = TransactionIdToPage(xid);
235 : 0 : TransactionIdSetPageStatus(xid, nsubxids_on_first_page, subxids, status,
236 : : lsn, pageno, false);
237 : :
238 : : /*
239 : : * Now work through the rest of the subxids one clog page at a time,
240 : : * starting from the second page onwards, like we did above.
241 : : */
242 : 0 : set_status_by_pages(nsubxids - nsubxids_on_first_page,
243 : 0 : subxids + nsubxids_on_first_page,
244 : : status, lsn);
245 : : }
6165 alvherre@alvh.no-ip. 246 :CBC 152100 : }
247 : :
248 : : /*
249 : : * Helper for TransactionIdSetTreeStatus: set the status for a bunch of
250 : : * transactions, chunking in the separate CLOG pages involved. We never
251 : : * pass the whole transaction tree to this function, only subtransactions
252 : : * that are on different pages to the top level transaction id.
253 : : */
254 : : static void
6165 alvherre@alvh.no-ip. 255 :UBC 0 : set_status_by_pages(int nsubxids, TransactionId *subxids,
256 : : XidStatus status, XLogRecPtr lsn)
257 : : {
647 akorotkov@postgresql 258 : 0 : int64 pageno = TransactionIdToPage(subxids[0]);
5931 bruce@momjian.us 259 : 0 : int offset = 0;
260 : 0 : int i = 0;
261 : :
2892 tgl@sss.pgh.pa.us 262 [ # # ]: 0 : Assert(nsubxids > 0); /* else the pageno fetch above is unsafe */
263 : :
6165 alvherre@alvh.no-ip. 264 [ # # ]: 0 : while (i < nsubxids)
265 : : {
5931 bruce@momjian.us 266 : 0 : int num_on_page = 0;
267 : : int64 nextpageno;
268 : :
269 : : do
270 : : {
2892 tgl@sss.pgh.pa.us 271 : 0 : nextpageno = TransactionIdToPage(subxids[i]);
272 [ # # ]: 0 : if (nextpageno != pageno)
273 : 0 : break;
6165 alvherre@alvh.no-ip. 274 : 0 : num_on_page++;
275 : 0 : i++;
2892 tgl@sss.pgh.pa.us 276 [ # # ]: 0 : } while (i < nsubxids);
277 : :
6165 alvherre@alvh.no-ip. 278 : 0 : TransactionIdSetPageStatus(InvalidTransactionId,
279 : 0 : num_on_page, subxids + offset,
280 : : status, lsn, pageno, false);
281 : 0 : offset = i;
2892 tgl@sss.pgh.pa.us 282 : 0 : pageno = nextpageno;
283 : : }
6165 alvherre@alvh.no-ip. 284 : 0 : }
285 : :
286 : : /*
287 : : * Record the final state of transaction entries in the commit log for all
288 : : * entries on a single page. Atomic only on this page.
289 : : */
290 : : static void
6165 alvherre@alvh.no-ip. 291 :CBC 152100 : TransactionIdSetPageStatus(TransactionId xid, int nsubxids,
292 : : TransactionId *subxids, XidStatus status,
293 : : XLogRecPtr lsn, int64 pageno,
294 : : bool all_xact_same_page)
295 : : {
296 : : LWLock *lock;
297 : :
298 : : /* Can't use group update when PGPROC overflows. */
299 : : StaticAssertDecl(THRESHOLD_SUBTRANS_CLOG_OPT <= PGPROC_MAX_CACHED_SUBXIDS,
300 : : "group clog threshold less than PGPROC cached subxids");
301 : :
302 : : /* Get the SLRU bank lock for the page we are going to access. */
556 303 : 152100 : lock = SimpleLruGetBankLock(XactCtl, pageno);
304 : :
305 : : /*
306 : : * When there is contention on the SLRU bank lock we need, we try to group
307 : : * multiple updates; a single leader process will perform transaction
308 : : * status updates for multiple backends so that the number of times the
309 : : * bank lock needs to be acquired is reduced.
310 : : *
311 : : * For this optimization to be safe, the XID and subxids in MyProc must be
312 : : * the same as the ones for which we're setting the status. Check that
313 : : * this is the case.
314 : : *
315 : : * For this optimization to be efficient, we shouldn't have too many
316 : : * sub-XIDs and all of the XIDs for which we're adjusting clog should be
317 : : * on the same page. Check those conditions, too.
318 : : */
1849 andres@anarazel.de 319 [ + - + + : 152100 : if (all_xact_same_page && xid == MyProc->xid &&
+ + ]
2927 rhaas@postgresql.org 320 : 127651 : nsubxids <= THRESHOLD_SUBTRANS_CLOG_OPT &&
1849 andres@anarazel.de 321 [ + - + + ]: 127651 : nsubxids == MyProc->subxidStatus.count &&
1283 tgl@sss.pgh.pa.us 322 : 455 : (nsubxids == 0 ||
323 [ + - ]: 455 : memcmp(subxids, MyProc->subxids.xids,
324 : : nsubxids * sizeof(TransactionId)) == 0))
325 : : {
326 : : /*
327 : : * If we can immediately acquire the lock, we update the status of our
328 : : * own XID and release the lock. If not, try use group XID update. If
329 : : * that doesn't work out, fall back to waiting for the lock to perform
330 : : * an update for this transaction only.
331 : : */
556 alvherre@alvh.no-ip. 332 [ + + ]: 127651 : if (LWLockConditionalAcquire(lock, LW_EXCLUSIVE))
333 : : {
334 : : /* Got the lock without waiting! Do the update. */
2927 rhaas@postgresql.org 335 : 127600 : TransactionIdSetPageStatusInternal(xid, nsubxids, subxids, status,
336 : : lsn, pageno);
556 alvherre@alvh.no-ip. 337 : 127600 : LWLockRelease(lock);
2927 rhaas@postgresql.org 338 : 127600 : return;
339 : : }
340 [ + - ]: 51 : else if (TransactionGroupUpdateXidStatus(xid, status, lsn, pageno))
341 : : {
342 : : /* Group update mechanism has done the work. */
343 : 51 : return;
344 : : }
345 : :
346 : : /* Fall through only if update isn't done yet. */
347 : : }
348 : :
349 : : /* Group update not applicable, or couldn't accept this page number. */
556 alvherre@alvh.no-ip. 350 : 24449 : LWLockAcquire(lock, LW_EXCLUSIVE);
2927 rhaas@postgresql.org 351 : 24449 : TransactionIdSetPageStatusInternal(xid, nsubxids, subxids, status,
352 : : lsn, pageno);
556 alvherre@alvh.no-ip. 353 : 24449 : LWLockRelease(lock);
354 : : }
355 : :
356 : : /*
357 : : * Record the final state of transaction entry in the commit log
358 : : *
359 : : * We don't do any locking here; caller must handle that.
360 : : */
361 : : static void
2927 rhaas@postgresql.org 362 : 152100 : TransactionIdSetPageStatusInternal(TransactionId xid, int nsubxids,
363 : : TransactionId *subxids, XidStatus status,
364 : : XLogRecPtr lsn, int64 pageno)
365 : : {
366 : : int slotno;
367 : : int i;
368 : :
8778 tgl@sss.pgh.pa.us 369 [ + + - + : 152100 : Assert(status == TRANSACTION_STATUS_COMMITTED ||
- - - - ]
370 : : status == TRANSACTION_STATUS_ABORTED ||
371 : : (status == TRANSACTION_STATUS_SUB_COMMITTED && !TransactionIdIsValid(xid)));
556 alvherre@alvh.no-ip. 372 [ - + ]: 152100 : Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(XactCtl, pageno),
373 : : LW_EXCLUSIVE));
374 : :
375 : : /*
376 : : * If we're doing an async commit (ie, lsn is valid), then we must wait
377 : : * for any active write on the page slot to complete. Otherwise our
378 : : * update could reach disk in that write, which will not do since we
379 : : * mustn't let it reach disk until we've done the appropriate WAL flush.
380 : : * But when lsn is invalid, it's OK to scribble on a page while it is
381 : : * write-busy, since we don't care if the update reaches disk sooner than
382 : : * we think.
383 : : */
1940 tgl@sss.pgh.pa.us 384 : 152100 : slotno = SimpleLruReadPage(XactCtl, pageno, XLogRecPtrIsInvalid(lsn), xid);
385 : :
386 : : /*
387 : : * Set the main transaction id, if any.
388 : : *
389 : : * If we update more than one xid on this page while it is being written
390 : : * out, we might find that some of the bits go to disk and others don't.
391 : : * If we are updating commits on the page with the top-level xid that
392 : : * could break atomicity, so we subcommit the subxids first before we mark
393 : : * the top-level commit.
394 : : */
6165 alvherre@alvh.no-ip. 395 [ + - ]: 152100 : if (TransactionIdIsValid(xid))
396 : : {
397 : : /* Subtransactions first, if needed ... */
398 [ + + ]: 152100 : if (status == TRANSACTION_STATUS_COMMITTED)
399 : : {
400 [ + + ]: 148142 : for (i = 0; i < nsubxids; i++)
401 : : {
1940 tgl@sss.pgh.pa.us 402 [ - + ]: 3785 : Assert(XactCtl->shared->page_number[slotno] == TransactionIdToPage(subxids[i]));
6165 alvherre@alvh.no-ip. 403 : 3785 : TransactionIdSetStatusBit(subxids[i],
404 : : TRANSACTION_STATUS_SUB_COMMITTED,
405 : : lsn, slotno);
406 : : }
407 : : }
408 : :
409 : : /* ... then the main transaction */
410 : 152100 : TransactionIdSetStatusBit(xid, status, lsn, slotno);
411 : : }
412 : :
413 : : /* Set the subtransactions */
414 [ + + ]: 156204 : for (i = 0; i < nsubxids; i++)
415 : : {
1940 tgl@sss.pgh.pa.us 416 [ - + ]: 4104 : Assert(XactCtl->shared->page_number[slotno] == TransactionIdToPage(subxids[i]));
6165 alvherre@alvh.no-ip. 417 : 4104 : TransactionIdSetStatusBit(subxids[i], status, lsn, slotno);
418 : : }
419 : :
1940 tgl@sss.pgh.pa.us 420 : 152100 : XactCtl->shared->page_dirty[slotno] = true;
2927 rhaas@postgresql.org 421 : 152100 : }
422 : :
423 : : /*
424 : : * Subroutine for TransactionIdSetPageStatus, q.v.
425 : : *
426 : : * When we cannot immediately acquire the SLRU bank lock in exclusive mode at
427 : : * commit time, add ourselves to a list of processes that need their XIDs
428 : : * status update. The first process to add itself to the list will acquire
429 : : * the lock in exclusive mode and set transaction status as required on behalf
430 : : * of all group members. This avoids a great deal of contention when many
431 : : * processes are trying to commit at once, since the lock need not be
432 : : * repeatedly handed off from one committing process to the next.
433 : : *
434 : : * Returns true when transaction status has been updated in clog; returns
435 : : * false if we decided against applying the optimization because the page
436 : : * number we need to update differs from those processes already waiting.
437 : : */
438 : : static bool
439 : 51 : TransactionGroupUpdateXidStatus(TransactionId xid, XidStatus status,
440 : : XLogRecPtr lsn, int64 pageno)
441 : : {
442 : 51 : volatile PROC_HDR *procglobal = ProcGlobal;
443 : 51 : PGPROC *proc = MyProc;
444 : : uint32 nextidx;
445 : : uint32 wakeidx;
446 : : int64 prevpageno;
556 alvherre@alvh.no-ip. 447 : 51 : LWLock *prevlock = NULL;
448 : :
449 : : /* We should definitely have an XID whose status needs to be updated. */
2927 rhaas@postgresql.org 450 [ - + ]: 51 : Assert(TransactionIdIsValid(xid));
451 : :
452 : : /*
453 : : * Prepare to add ourselves to the list of processes needing a group XID
454 : : * status update.
455 : : */
456 : 51 : proc->clogGroupMember = true;
457 : 51 : proc->clogGroupMemberXid = xid;
458 : 51 : proc->clogGroupMemberXidStatus = status;
459 : 51 : proc->clogGroupMemberPage = pageno;
460 : 51 : proc->clogGroupMemberLsn = lsn;
461 : :
462 : : /*
463 : : * We put ourselves in the queue by writing MyProcNumber to
464 : : * ProcGlobal->clogGroupFirst. However, if there's already a process
465 : : * listed there, we compare our pageno with that of that process; if it
466 : : * differs, we cannot participate in the group, so we return for caller to
467 : : * update pg_xact in the normal way.
468 : : *
469 : : * If we're not the first process in the list, we must follow the leader.
470 : : * We do this by storing the data we want updated in our PGPROC entry
471 : : * where the leader can find it, then going to sleep.
472 : : *
473 : : * If no process is already in the list, we're the leader; our first step
474 : : * is to lock the SLRU bank to which our page belongs, then we close out
475 : : * the group by resetting the list pointer from ProcGlobal->clogGroupFirst
476 : : * (this lets other processes set up other groups later); finally we do
477 : : * the SLRU updates, release the SLRU bank lock, and wake up the sleeping
478 : : * processes.
479 : : *
480 : : * If another group starts to update a page in a different SLRU bank, they
481 : : * can proceed concurrently, since the bank lock they're going to use is
482 : : * different from ours. If another group starts to update a page in the
483 : : * same bank as ours, they wait until we release the lock.
484 : : */
485 : 51 : nextidx = pg_atomic_read_u32(&procglobal->clogGroupFirst);
486 : :
487 : : while (true)
488 : : {
489 : : /*
490 : : * Add the proc to list, if the clog page where we need to update the
491 : : * current transaction status is same as group leader's clog page.
492 : : *
493 : : * There is a race condition here, which is that after doing the below
494 : : * check and before adding this proc's clog update to a group, the
495 : : * group leader might have already finished the group update for this
496 : : * page and becomes group leader of another group, updating a
497 : : * different page. This will lead to a situation where a single group
498 : : * can have different clog page updates. This isn't likely and will
499 : : * still work, just less efficiently -- we handle this case by
500 : : * switching to a different bank lock in the loop below.
501 : : */
552 heikki.linnakangas@i 502 [ + + ]: 52 : if (nextidx != INVALID_PROC_NUMBER &&
562 503 [ - + ]: 6 : GetPGProcByNumber(nextidx)->clogGroupMemberPage != proc->clogGroupMemberPage)
504 : : {
505 : : /*
506 : : * Ensure that this proc is not a member of any clog group that
507 : : * needs an XID status update.
508 : : */
2927 rhaas@postgresql.org 509 :UBC 0 : proc->clogGroupMember = false;
552 heikki.linnakangas@i 510 : 0 : pg_atomic_write_u32(&proc->clogGroupNext, INVALID_PROC_NUMBER);
2927 rhaas@postgresql.org 511 : 0 : return false;
512 : : }
513 : :
2927 rhaas@postgresql.org 514 :CBC 52 : pg_atomic_write_u32(&proc->clogGroupNext, nextidx);
515 : :
516 [ + + ]: 52 : if (pg_atomic_compare_exchange_u32(&procglobal->clogGroupFirst,
517 : : &nextidx,
518 : : (uint32) MyProcNumber))
519 : 51 : break;
520 : : }
521 : :
522 : : /*
523 : : * If the list was not empty, the leader will update the status of our
524 : : * XID. It is impossible to have followers without a leader because the
525 : : * first process that has added itself to the list will always have
526 : : * nextidx as INVALID_PROC_NUMBER.
527 : : */
552 heikki.linnakangas@i 528 [ + + ]: 51 : if (nextidx != INVALID_PROC_NUMBER)
529 : : {
2927 rhaas@postgresql.org 530 : 6 : int extraWaits = 0;
531 : :
532 : : /* Sleep until the leader updates our XID status. */
1939 tgl@sss.pgh.pa.us 533 : 6 : pgstat_report_wait_start(WAIT_EVENT_XACT_GROUP_UPDATE);
534 : : for (;;)
535 : : {
536 : : /* acts as a read barrier */
2927 rhaas@postgresql.org 537 : 6 : PGSemaphoreLock(proc->sem);
538 [ + - ]: 6 : if (!proc->clogGroupMember)
539 : 6 : break;
2927 rhaas@postgresql.org 540 :UBC 0 : extraWaits++;
541 : : }
2927 rhaas@postgresql.org 542 :CBC 6 : pgstat_report_wait_end();
543 : :
552 heikki.linnakangas@i 544 [ - + ]: 6 : Assert(pg_atomic_read_u32(&proc->clogGroupNext) == INVALID_PROC_NUMBER);
545 : :
546 : : /* Fix semaphore count for any absorbed wakeups */
2927 rhaas@postgresql.org 547 [ - + ]: 6 : while (extraWaits-- > 0)
2927 rhaas@postgresql.org 548 :UBC 0 : PGSemaphoreUnlock(proc->sem);
2927 rhaas@postgresql.org 549 :CBC 6 : return true;
550 : : }
551 : :
552 : : /*
553 : : * By here, we know we're the leader process. Acquire the SLRU bank lock
554 : : * that corresponds to the page we originally wanted to modify.
555 : : */
556 alvherre@alvh.no-ip. 556 : 45 : prevpageno = proc->clogGroupMemberPage;
557 : 45 : prevlock = SimpleLruGetBankLock(XactCtl, prevpageno);
558 : 45 : LWLockAcquire(prevlock, LW_EXCLUSIVE);
559 : :
560 : : /*
561 : : * Now that we've got the lock, clear the list of processes waiting for
562 : : * group XID status update, saving a pointer to the head of the list.
563 : : * (Trying to pop elements one at a time could lead to an ABA problem.)
564 : : *
565 : : * At this point, any processes trying to do this would create a separate
566 : : * group.
567 : : */
2927 rhaas@postgresql.org 568 : 45 : nextidx = pg_atomic_exchange_u32(&procglobal->clogGroupFirst,
569 : : INVALID_PROC_NUMBER);
570 : :
571 : : /* Remember head of list so we can perform wakeups after dropping lock. */
572 : 45 : wakeidx = nextidx;
573 : :
574 : : /* Walk the list and update the status of all XIDs. */
552 heikki.linnakangas@i 575 [ + + ]: 96 : while (nextidx != INVALID_PROC_NUMBER)
576 : : {
1067 drowley@postgresql.o 577 : 51 : PGPROC *nextproc = &ProcGlobal->allProcs[nextidx];
410 michael@paquier.xyz 578 : 51 : int64 thispageno = nextproc->clogGroupMemberPage;
579 : :
580 : : /*
581 : : * If the page to update belongs to a different bank than the previous
582 : : * one, exchange bank lock to the new one. This should be quite rare,
583 : : * as described above.
584 : : *
585 : : * (We could try to optimize this by waking up the processes for which
586 : : * we have already updated the status while we exchange the lock, but
587 : : * the code doesn't do that at present. I think it'd require
588 : : * additional bookkeeping, making the common path slower in order to
589 : : * improve an infrequent case.)
590 : : */
556 alvherre@alvh.no-ip. 591 [ - + ]: 51 : if (thispageno != prevpageno)
592 : : {
556 alvherre@alvh.no-ip. 593 :UBC 0 : LWLock *lock = SimpleLruGetBankLock(XactCtl, thispageno);
594 : :
595 [ # # ]: 0 : if (prevlock != lock)
596 : : {
597 : 0 : LWLockRelease(prevlock);
598 : 0 : LWLockAcquire(lock, LW_EXCLUSIVE);
599 : : }
600 : 0 : prevlock = lock;
601 : 0 : prevpageno = thispageno;
602 : : }
603 : :
604 : : /*
605 : : * Transactions with more than THRESHOLD_SUBTRANS_CLOG_OPT sub-XIDs
606 : : * should not use group XID status update mechanism.
607 : : */
1067 drowley@postgresql.o 608 [ - + ]:CBC 51 : Assert(nextproc->subxidStatus.count <= THRESHOLD_SUBTRANS_CLOG_OPT);
609 : :
610 : 51 : TransactionIdSetPageStatusInternal(nextproc->clogGroupMemberXid,
611 : 51 : nextproc->subxidStatus.count,
612 : 51 : nextproc->subxids.xids,
613 : : nextproc->clogGroupMemberXidStatus,
614 : : nextproc->clogGroupMemberLsn,
615 : : nextproc->clogGroupMemberPage);
616 : :
617 : : /* Move to next proc in list. */
618 : 51 : nextidx = pg_atomic_read_u32(&nextproc->clogGroupNext);
619 : : }
620 : :
621 : : /* We're done with the lock now. */
556 alvherre@alvh.no-ip. 622 [ + - ]: 45 : if (prevlock != NULL)
623 : 45 : LWLockRelease(prevlock);
624 : :
625 : : /*
626 : : * Now that we've released the lock, go back and wake everybody up. We
627 : : * don't do this under the lock so as to keep lock hold times to a
628 : : * minimum.
629 : : *
630 : : * (Perhaps we could do this in two passes, the first setting
631 : : * clogGroupNext to invalid while saving the semaphores to an array, then
632 : : * a single write barrier, then another pass unlocking the semaphores.)
633 : : */
552 heikki.linnakangas@i 634 [ + + ]: 96 : while (wakeidx != INVALID_PROC_NUMBER)
635 : : {
1067 drowley@postgresql.o 636 : 51 : PGPROC *wakeproc = &ProcGlobal->allProcs[wakeidx];
637 : :
638 : 51 : wakeidx = pg_atomic_read_u32(&wakeproc->clogGroupNext);
552 heikki.linnakangas@i 639 : 51 : pg_atomic_write_u32(&wakeproc->clogGroupNext, INVALID_PROC_NUMBER);
640 : :
641 : : /* ensure all previous writes are visible before follower continues. */
2927 rhaas@postgresql.org 642 : 51 : pg_write_barrier();
643 : :
1067 drowley@postgresql.o 644 : 51 : wakeproc->clogGroupMember = false;
645 : :
646 [ + + ]: 51 : if (wakeproc != MyProc)
647 : 6 : PGSemaphoreUnlock(wakeproc->sem);
648 : : }
649 : :
2927 rhaas@postgresql.org 650 : 45 : return true;
651 : : }
652 : :
653 : : /*
654 : : * Sets the commit status of a single transaction.
655 : : *
656 : : * Caller must hold the corresponding SLRU bank lock, will be held at exit.
657 : : */
658 : : static void
6165 alvherre@alvh.no-ip. 659 : 159989 : TransactionIdSetStatusBit(TransactionId xid, XidStatus status, XLogRecPtr lsn, int slotno)
660 : : {
661 : 159989 : int byteno = TransactionIdToByte(xid);
662 : 159989 : int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
663 : : char *byteptr;
664 : : char byteval;
665 : : char curval;
666 : :
556 667 [ - + ]: 159989 : Assert(XactCtl->shared->page_number[slotno] == TransactionIdToPage(xid));
668 [ - + ]: 159989 : Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(XactCtl,
669 : : XactCtl->shared->page_number[slotno]),
670 : : LW_EXCLUSIVE));
671 : :
1940 tgl@sss.pgh.pa.us 672 : 159989 : byteptr = XactCtl->shared->page_buffer[slotno] + byteno;
6151 alvherre@alvh.no-ip. 673 : 159989 : curval = (*byteptr >> bshift) & CLOG_XACT_BITMASK;
674 : :
675 : : /*
676 : : * When replaying transactions during recovery we still need to perform
677 : : * the two phases of subcommit and then commit. However, some transactions
678 : : * are already correctly marked, so we just treat those as a no-op which
679 : : * allows us to keep the following Assert as restrictive as possible.
680 : : */
681 [ + + + + : 159989 : if (InRecovery && status == TRANSACTION_STATUS_SUB_COMMITTED &&
- + ]
682 : : curval == TRANSACTION_STATUS_COMMITTED)
6151 alvherre@alvh.no-ip. 683 :UBC 0 : return;
684 : :
685 : : /*
686 : : * Current state change should be from 0 or subcommitted to target state
687 : : * or we should already be there when replaying changes during recovery.
688 : : */
6151 alvherre@alvh.no-ip. 689 [ + + + + :CBC 159989 : Assert(curval == 0 ||
- + - + ]
690 : : (curval == TRANSACTION_STATUS_SUB_COMMITTED &&
691 : : status != TRANSACTION_STATUS_IN_PROGRESS) ||
692 : : curval == status);
693 : :
694 : : /* note this assumes exclusive access to the clog page */
7735 tgl@sss.pgh.pa.us 695 : 159989 : byteval = *byteptr;
696 : 159989 : byteval &= ~(((1 << CLOG_BITS_PER_XACT) - 1) << bshift);
697 : 159989 : byteval |= (status << bshift);
698 : 159989 : *byteptr = byteval;
699 : :
700 : : /*
701 : : * Update the group LSN if the transaction completion LSN is higher.
702 : : *
703 : : * Note: lsn will be invalid when supplied during InRecovery processing,
704 : : * so we don't need to do anything special to avoid LSN updates during
705 : : * recovery. After recovery completes the next clog change will set the
706 : : * LSN correctly.
707 : : */
6611 708 [ + + ]: 159989 : if (!XLogRecPtrIsInvalid(lsn))
709 : : {
710 : 28279 : int lsnindex = GetLSNIndex(slotno, xid);
711 : :
1940 712 [ + + ]: 28279 : if (XactCtl->shared->group_lsn[lsnindex] < lsn)
713 : 25665 : XactCtl->shared->group_lsn[lsnindex] = lsn;
714 : : }
715 : : }
716 : :
717 : : /*
718 : : * Interrogate the state of a transaction in the commit log.
719 : : *
720 : : * Aside from the actual commit status, this function returns (into *lsn)
721 : : * an LSN that is late enough to be able to guarantee that if we flush up to
722 : : * that LSN then we will have flushed the transaction's commit record to disk.
723 : : * The result is not necessarily the exact LSN of the transaction's commit
724 : : * record! For example, for long-past transactions (those whose clog pages
725 : : * already migrated to disk), we'll return InvalidXLogRecPtr. Also, because
726 : : * we group transactions on the same clog page to conserve storage, we might
727 : : * return the LSN of a later transaction that falls into the same group.
728 : : *
729 : : * NB: this is a low-level routine and is NOT the preferred entry point
730 : : * for most uses; TransactionLogFetch() in transam.c is the intended caller.
731 : : */
732 : : XidStatus
6611 733 : 703878 : TransactionIdGetStatus(TransactionId xid, XLogRecPtr *lsn)
734 : : {
647 akorotkov@postgresql 735 : 703878 : int64 pageno = TransactionIdToPage(xid);
8778 tgl@sss.pgh.pa.us 736 : 703878 : int byteno = TransactionIdToByte(xid);
737 : 703878 : int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
738 : : int slotno;
739 : : int lsnindex;
740 : : char *byteptr;
741 : : XidStatus status;
742 : :
743 : : /* lock is acquired by SimpleLruReadPage_ReadOnly */
744 : :
1940 745 : 703878 : slotno = SimpleLruReadPage_ReadOnly(XactCtl, pageno, xid);
746 : 703878 : byteptr = XactCtl->shared->page_buffer[slotno] + byteno;
747 : :
8778 748 : 703878 : status = (*byteptr >> bshift) & CLOG_XACT_BITMASK;
749 : :
6611 750 : 703878 : lsnindex = GetLSNIndex(slotno, xid);
1940 751 : 703878 : *lsn = XactCtl->shared->group_lsn[lsnindex];
752 : :
556 alvherre@alvh.no-ip. 753 : 703878 : LWLockRelease(SimpleLruGetBankLock(XactCtl, pageno));
754 : :
8778 tgl@sss.pgh.pa.us 755 : 703878 : return status;
756 : : }
757 : :
758 : : /*
759 : : * Number of shared CLOG buffers.
760 : : *
761 : : * If asked to autotune, use 2MB for every 1GB of shared buffers, up to 8MB.
762 : : * Otherwise just cap the configured amount to be between 16 and the maximum
763 : : * allowed.
764 : : */
765 : : static int
4992 rhaas@postgresql.org 766 : 3963 : CLOGShmemBuffers(void)
767 : : {
768 : : /* auto-tune based on shared buffers */
556 alvherre@alvh.no-ip. 769 [ + + ]: 3963 : if (transaction_buffers == 0)
770 : 2930 : return SimpleLruAutotuneBuffers(512, 1024);
771 : :
772 [ + - + - ]: 1033 : return Min(Max(16, transaction_buffers), CLOG_MAX_ALLOWED_BUFFERS);
773 : : }
774 : :
775 : : /*
776 : : * Initialization of shared memory for CLOG
777 : : */
778 : : Size
8778 tgl@sss.pgh.pa.us 779 : 1909 : CLOGShmemSize(void)
780 : : {
4992 rhaas@postgresql.org 781 : 1909 : return SimpleLruShmemSize(CLOGShmemBuffers(), CLOG_LSNS_PER_PAGE);
782 : : }
783 : :
784 : : void
8778 tgl@sss.pgh.pa.us 785 : 1029 : CLOGShmemInit(void)
786 : : {
787 : : /* If auto-tuning is requested, now is the time to do it */
556 alvherre@alvh.no-ip. 788 [ + + ]: 1029 : if (transaction_buffers == 0)
789 : : {
790 : : char buf[32];
791 : :
792 : 1025 : snprintf(buf, sizeof(buf), "%d", CLOGShmemBuffers());
793 : 1025 : SetConfigOption("transaction_buffers", buf, PGC_POSTMASTER,
794 : : PGC_S_DYNAMIC_DEFAULT);
795 : :
796 : : /*
797 : : * We prefer to report this value's source as PGC_S_DYNAMIC_DEFAULT.
798 : : * However, if the DBA explicitly set transaction_buffers = 0 in the
799 : : * config file, then PGC_S_DYNAMIC_DEFAULT will fail to override that
800 : : * and we must force the matter with PGC_S_OVERRIDE.
801 : : */
802 [ - + ]: 1025 : if (transaction_buffers == 0) /* failed to apply it? */
556 alvherre@alvh.no-ip. 803 :UBC 0 : SetConfigOption("transaction_buffers", buf, PGC_POSTMASTER,
804 : : PGC_S_OVERRIDE);
805 : : }
556 alvherre@alvh.no-ip. 806 [ - + ]:CBC 1029 : Assert(transaction_buffers != 0);
807 : :
1940 tgl@sss.pgh.pa.us 808 : 1029 : XactCtl->PagePrecedes = CLOGPagePrecedes;
556 alvherre@alvh.no-ip. 809 : 1029 : SimpleLruInit(XactCtl, "transaction", CLOGShmemBuffers(), CLOG_LSNS_PER_PAGE,
810 : : "pg_xact", LWTRANCHE_XACT_BUFFER,
811 : : LWTRANCHE_XACT_SLRU, SYNC_HANDLER_CLOG, false);
1694 noah@leadboat.com 812 : 1029 : SlruPagePrecedesUnitTests(XactCtl, CLOG_XACTS_PER_PAGE);
8778 tgl@sss.pgh.pa.us 813 : 1029 : }
814 : :
815 : : /*
816 : : * GUC check_hook for transaction_buffers
817 : : */
818 : : bool
556 alvherre@alvh.no-ip. 819 : 2092 : check_transaction_buffers(int *newval, void **extra, GucSource source)
820 : : {
821 : 2092 : return check_slru_buffers("transaction_buffers", newval);
822 : : }
823 : :
824 : : /*
825 : : * This func must be called ONCE on system install. It creates
826 : : * the initial CLOG segment. (The CLOG directory is assumed to
827 : : * have been created by initdb, and CLOGShmemInit must have been
828 : : * called already.)
829 : : */
830 : : void
8778 tgl@sss.pgh.pa.us 831 : 50 : BootStrapCLOG(void)
832 : : {
833 : : /* Zero the initial page and flush it to disk */
61 alvherre@kurilemu.de 834 :GNC 50 : SimpleLruZeroAndWritePage(XactCtl, 0);
8778 tgl@sss.pgh.pa.us 835 :GIC 50 : }
836 : :
837 : : /*
838 : : * This must be called ONCE during postmaster or standalone-backend startup,
839 : : * after StartupXLOG has initialized TransamVariables->nextXid.
840 : : */
841 : : void
8778 tgl@sss.pgh.pa.us 842 :CBC 887 : StartupCLOG(void)
843 : : {
638 heikki.linnakangas@i 844 : 887 : TransactionId xid = XidFromFullTransactionId(TransamVariables->nextXid);
647 akorotkov@postgresql 845 : 887 : int64 pageno = TransactionIdToPage(xid);
846 : :
847 : : /*
848 : : * Initialize our idea of the latest page number.
849 : : */
578 alvherre@alvh.no-ip. 850 : 887 : pg_atomic_write_u64(&XactCtl->shared->latest_page_number, pageno);
5057 simon@2ndQuadrant.co 851 : 887 : }
852 : :
853 : : /*
854 : : * This must be called ONCE at the end of startup/recovery.
855 : : */
856 : : void
857 : 832 : TrimCLOG(void)
858 : : {
638 heikki.linnakangas@i 859 : 832 : TransactionId xid = XidFromFullTransactionId(TransamVariables->nextXid);
647 akorotkov@postgresql 860 : 832 : int64 pageno = TransactionIdToPage(xid);
556 alvherre@alvh.no-ip. 861 : 832 : LWLock *lock = SimpleLruGetBankLock(XactCtl, pageno);
862 : :
863 : 832 : LWLockAcquire(lock, LW_EXCLUSIVE);
864 : :
865 : : /*
866 : : * Zero out the remainder of the current clog page. Under normal
867 : : * circumstances it should be zeroes already, but it seems at least
868 : : * theoretically possible that XLOG replay will have settled on a nextXID
869 : : * value that is less than the last XID actually used and marked by the
870 : : * previous database lifecycle (since subtransaction commit writes clog
871 : : * but makes no WAL entry). Let's just be safe. (We need not worry about
872 : : * pages beyond the current one, since those will be zeroed when first
873 : : * used. For the same reason, there is no need to do anything when
874 : : * nextXid is exactly at a page boundary; and it's likely that the
875 : : * "current" page doesn't exist yet in that case.)
876 : : */
7563 tgl@sss.pgh.pa.us 877 [ + + ]: 832 : if (TransactionIdToPgIndex(xid) != 0)
878 : : {
879 : 831 : int byteno = TransactionIdToByte(xid);
880 : 831 : int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
881 : : int slotno;
882 : : char *byteptr;
883 : :
1940 884 : 831 : slotno = SimpleLruReadPage(XactCtl, pageno, false, xid);
885 : 831 : byteptr = XactCtl->shared->page_buffer[slotno] + byteno;
886 : :
887 : : /* Zero so-far-unused positions in the current byte */
7563 888 : 831 : *byteptr &= (1 << bshift) - 1;
889 : : /* Zero the rest of the page */
890 [ + + + - : 831 : MemSet(byteptr + 1, 0, BLCKSZ - byteno - 1);
+ - - + -
- ]
891 : :
1940 892 : 831 : XactCtl->shared->page_dirty[slotno] = true;
893 : : }
894 : :
556 alvherre@alvh.no-ip. 895 : 832 : LWLockRelease(lock);
8778 tgl@sss.pgh.pa.us 896 : 832 : }
897 : :
898 : : /*
899 : : * Perform a checkpoint --- either during shutdown, or on-the-fly
900 : : */
901 : : void
902 : 1677 : CheckPointCLOG(void)
903 : : {
904 : : /*
905 : : * Write dirty CLOG pages to disk. This may result in sync requests
906 : : * queued for later handling by ProcessSyncRequests(), as part of the
907 : : * checkpoint.
908 : : */
909 : : TRACE_POSTGRESQL_CLOG_CHECKPOINT_START(true);
1807 tmunro@postgresql.or 910 : 1677 : SimpleLruWriteAll(XactCtl, true);
911 : : TRACE_POSTGRESQL_CLOG_CHECKPOINT_DONE(true);
8778 tgl@sss.pgh.pa.us 912 : 1677 : }
913 : :
914 : :
915 : : /*
916 : : * Make sure that CLOG has room for a newly-allocated XID.
917 : : *
918 : : * NB: this is called while holding XidGenLock. We want it to be very fast
919 : : * most of the time; even when it's not so fast, no actual I/O need happen
920 : : * unless we're forced to write out a dirty clog or xlog page to make room
921 : : * in shared memory.
922 : : */
923 : : void
924 : 131306 : ExtendCLOG(TransactionId newestXact)
925 : : {
926 : : int64 pageno;
927 : : LWLock *lock;
928 : :
929 : : /*
930 : : * No work except at first XID of a page. But beware: just after
931 : : * wraparound, the first XID of page zero is FirstNormalTransactionId.
932 : : */
8777 933 [ + - + + ]: 131306 : if (TransactionIdToPgIndex(newestXact) != 0 &&
934 : : !TransactionIdEquals(newestXact, FirstNormalTransactionId))
8778 935 : 131258 : return;
936 : :
937 : 48 : pageno = TransactionIdToPage(newestXact);
556 alvherre@alvh.no-ip. 938 : 48 : lock = SimpleLruGetBankLock(XactCtl, pageno);
939 : :
940 : 48 : LWLockAcquire(lock, LW_EXCLUSIVE);
941 : :
942 : : /* Zero the page and make a WAL entry about it */
61 alvherre@kurilemu.de 943 :GNC 48 : SimpleLruZeroPage(XactCtl, pageno);
944 : 48 : XLogSimpleInsertInt64(RM_CLOG_ID, CLOG_ZEROPAGE, pageno);
945 : :
556 alvherre@alvh.no-ip. 946 :CBC 48 : LWLockRelease(lock);
947 : : }
948 : :
949 : :
950 : : /*
951 : : * Remove all CLOG segments before the one holding the passed transaction ID
952 : : *
953 : : * Before removing any CLOG data, we must flush XLOG to disk, to ensure that
954 : : * any recently-emitted records with freeze plans have reached disk; otherwise
955 : : * a crash and restart might leave us with some unfrozen tuples referencing
956 : : * removed CLOG data. We choose to emit a special TRUNCATE XLOG record too.
957 : : * Replaying the deletion from XLOG is not critical, since the files could
958 : : * just as well be removed later, but doing so prevents a long-running hot
959 : : * standby server from acquiring an unreasonably bloated CLOG directory.
960 : : *
961 : : * Since CLOG segments hold a large number of transactions, the opportunity to
962 : : * actually remove a segment is fairly rare, and so it seems best not to do
963 : : * the XLOG flush unless we have confirmed that there is a removable segment.
964 : : */
965 : : void
3089 rhaas@postgresql.org 966 : 98 : TruncateCLOG(TransactionId oldestXact, Oid oldestxid_datoid)
967 : : {
968 : : int64 cutoffPage;
969 : :
970 : : /*
971 : : * The cutoff point is the start of the segment containing oldestXact. We
972 : : * pass the *page* containing oldestXact to SimpleLruTruncate.
973 : : */
8778 tgl@sss.pgh.pa.us 974 : 98 : cutoffPage = TransactionIdToPage(oldestXact);
975 : :
976 : : /* Check to see if there's any files that could be removed */
1940 977 [ + - ]: 98 : if (!SlruScanDirectory(XactCtl, SlruScanDirCbReportPresence, &cutoffPage))
7684 978 : 98 : return; /* nothing to remove */
979 : :
980 : : /*
981 : : * Advance oldestClogXid before truncating clog, so concurrent xact status
982 : : * lookups can ensure they don't attempt to access truncated-away clog.
983 : : *
984 : : * It's only necessary to do this if we will actually truncate away clog
985 : : * pages.
986 : : */
3089 rhaas@postgresql.org 987 :UBC 0 : AdvanceOldestClogXid(oldestXact);
988 : :
989 : : /*
990 : : * Write XLOG record and flush XLOG to disk. We record the oldest xid
991 : : * we're keeping information about here so we can ensure that it's always
992 : : * ahead of clog truncation in case we crash, and so a standby finds out
993 : : * the new valid xid before the next checkpoint.
994 : : */
995 : 0 : WriteTruncateXlogRec(cutoffPage, oldestXact, oldestxid_datoid);
996 : :
997 : : /* Now we can remove the old CLOG segment(s) */
1940 tgl@sss.pgh.pa.us 998 : 0 : SimpleLruTruncate(XactCtl, cutoffPage);
999 : : }
1000 : :
1001 : :
1002 : : /*
1003 : : * Decide whether a CLOG page number is "older" for truncation purposes.
1004 : : *
1005 : : * We need to use comparison of TransactionIds here in order to do the right
1006 : : * thing with wraparound XID arithmetic. However, TransactionIdPrecedes()
1007 : : * would get weird about permanent xact IDs. So, offset both such that xid1,
1008 : : * xid2, and xid2 + CLOG_XACTS_PER_PAGE - 1 are all normal XIDs; this offset
1009 : : * is relevant to page 0 and to the page preceding page 0.
1010 : : *
1011 : : * The page containing oldestXact-2^31 is the important edge case. The
1012 : : * portion of that page equaling or following oldestXact-2^31 is expendable,
1013 : : * but the portion preceding oldestXact-2^31 is not. When oldestXact-2^31 is
1014 : : * the first XID of a page and segment, the entire page and segment is
1015 : : * expendable, and we could truncate the segment. Recognizing that case would
1016 : : * require making oldestXact, not just the page containing oldestXact,
1017 : : * available to this callback. The benefit would be rare and small, so we
1018 : : * don't optimize that edge case.
1019 : : */
1020 : : static bool
647 akorotkov@postgresql 1021 :CBC 40229 : CLOGPagePrecedes(int64 page1, int64 page2)
1022 : : {
1023 : : TransactionId xid1;
1024 : : TransactionId xid2;
1025 : :
8717 tgl@sss.pgh.pa.us 1026 : 40229 : xid1 = ((TransactionId) page1) * CLOG_XACTS_PER_PAGE;
1694 noah@leadboat.com 1027 : 40229 : xid1 += FirstNormalTransactionId + 1;
8717 tgl@sss.pgh.pa.us 1028 : 40229 : xid2 = ((TransactionId) page2) * CLOG_XACTS_PER_PAGE;
1694 noah@leadboat.com 1029 : 40229 : xid2 += FirstNormalTransactionId + 1;
1030 : :
1031 [ + + + + ]: 66983 : return (TransactionIdPrecedes(xid1, xid2) &&
1032 : 26754 : TransactionIdPrecedes(xid1, xid2 + CLOG_XACTS_PER_PAGE - 1));
1033 : : }
1034 : :
1035 : :
1036 : : /*
1037 : : * Write a TRUNCATE xlog record
1038 : : *
1039 : : * We must flush the xlog record to disk before returning --- see notes
1040 : : * in TruncateCLOG().
1041 : : */
1042 : : static void
647 akorotkov@postgresql 1043 :UBC 0 : WriteTruncateXlogRec(int64 pageno, TransactionId oldestXact, Oid oldestXactDb)
1044 : : {
1045 : : XLogRecPtr recptr;
1046 : : xl_clog_truncate xlrec;
1047 : :
3089 rhaas@postgresql.org 1048 : 0 : xlrec.pageno = pageno;
1049 : 0 : xlrec.oldestXact = oldestXact;
1050 : 0 : xlrec.oldestXactDb = oldestXactDb;
1051 : :
3943 heikki.linnakangas@i 1052 : 0 : XLogBeginInsert();
207 peter@eisentraut.org 1053 : 0 : XLogRegisterData(&xlrec, sizeof(xl_clog_truncate));
3943 heikki.linnakangas@i 1054 : 0 : recptr = XLogInsert(RM_CLOG_ID, CLOG_TRUNCATE);
6880 tgl@sss.pgh.pa.us 1055 : 0 : XLogFlush(recptr);
1056 : 0 : }
1057 : :
1058 : : /*
1059 : : * CLOG resource manager's routines
1060 : : */
1061 : : void
3943 heikki.linnakangas@i 1062 : 0 : clog_redo(XLogReaderState *record)
1063 : : {
1064 : 0 : uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
1065 : :
1066 : : /* Backup blocks are not used in clog records */
1067 [ # # ]: 0 : Assert(!XLogRecHasAnyBlockRefs(record));
1068 : :
7684 tgl@sss.pgh.pa.us 1069 [ # # ]: 0 : if (info == CLOG_ZEROPAGE)
1070 : : {
1071 : : int64 pageno;
1072 : :
647 akorotkov@postgresql 1073 : 0 : memcpy(&pageno, XLogRecGetData(record), sizeof(pageno));
61 alvherre@kurilemu.de 1074 :UNC 0 : SimpleLruZeroAndWritePage(XactCtl, pageno);
1075 : : }
6880 tgl@sss.pgh.pa.us 1076 [ # # ]:UBC 0 : else if (info == CLOG_TRUNCATE)
1077 : : {
1078 : : xl_clog_truncate xlrec;
1079 : :
3089 rhaas@postgresql.org 1080 : 0 : memcpy(&xlrec, XLogRecGetData(record), sizeof(xl_clog_truncate));
1081 : :
1082 : 0 : AdvanceOldestClogXid(xlrec.oldestXact);
1083 : :
1940 tgl@sss.pgh.pa.us 1084 : 0 : SimpleLruTruncate(XactCtl, xlrec.pageno);
1085 : : }
1086 : : else
6880 1087 [ # # ]: 0 : elog(PANIC, "clog_redo: unknown op code %u", info);
7684 1088 : 0 : }
1089 : :
1090 : : /*
1091 : : * Entrypoint for sync.c to sync clog files.
1092 : : */
1093 : : int
1807 tmunro@postgresql.or 1094 : 0 : clogsyncfiletag(const FileTag *ftag, char *path)
1095 : : {
1096 : 0 : return SlruSyncFileTag(XactCtl, ftag, path);
1097 : : }
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