Age Owner Branch data TLA Line data Source code
1 : : /*----------------------------------------------------------------------
2 : : *
3 : : * tableam.c
4 : : * Table access method routines too big to be inline functions.
5 : : *
6 : : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
7 : : * Portions Copyright (c) 1994, Regents of the University of California
8 : : *
9 : : *
10 : : * IDENTIFICATION
11 : : * src/backend/access/table/tableam.c
12 : : *
13 : : * NOTES
14 : : * Note that most functions in here are documented in tableam.h, rather than
15 : : * here. That's because there's a lot of inline functions in tableam.h and
16 : : * it'd be harder to understand if one constantly had to switch between files.
17 : : *
18 : : *----------------------------------------------------------------------
19 : : */
20 : : #include "postgres.h"
21 : :
22 : : #include <math.h>
23 : :
24 : : #include "access/syncscan.h"
25 : : #include "access/tableam.h"
26 : : #include "access/xact.h"
27 : : #include "optimizer/optimizer.h"
28 : : #include "optimizer/plancat.h"
29 : : #include "port/pg_bitutils.h"
30 : : #include "storage/bufmgr.h"
31 : : #include "storage/shmem.h"
32 : : #include "storage/smgr.h"
33 : :
34 : : /*
35 : : * Constants to control the behavior of block allocation to parallel workers
36 : : * during a parallel seqscan. Technically these values do not need to be
37 : : * powers of 2, but having them as powers of 2 makes the math more optimal
38 : : * and makes the ramp-down stepping more even.
39 : : */
40 : :
41 : : /* The number of I/O chunks we try to break a parallel seqscan down into */
42 : : #define PARALLEL_SEQSCAN_NCHUNKS 2048
43 : : /* Ramp down size of allocations when we've only this number of chunks left */
44 : : #define PARALLEL_SEQSCAN_RAMPDOWN_CHUNKS 64
45 : : /* Cap the size of parallel I/O chunks to this number of blocks */
46 : : #define PARALLEL_SEQSCAN_MAX_CHUNK_SIZE 8192
47 : :
48 : : /* GUC variables */
49 : : char *default_table_access_method = DEFAULT_TABLE_ACCESS_METHOD;
50 : : bool synchronize_seqscans = true;
51 : :
52 : :
53 : : /* ----------------------------------------------------------------------------
54 : : * Slot functions.
55 : : * ----------------------------------------------------------------------------
56 : : */
57 : :
58 : : const TupleTableSlotOps *
2561 andres@anarazel.de 59 :CBC 14593996 : table_slot_callbacks(Relation relation)
60 : : {
61 : : const TupleTableSlotOps *tts_cb;
62 : :
63 [ + + ]: 14593996 : if (relation->rd_tableam)
64 : 14590104 : tts_cb = relation->rd_tableam->slot_callbacks(relation);
65 [ + + ]: 3892 : else if (relation->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
66 : : {
67 : : /*
68 : : * Historically FDWs expect to store heap tuples in slots. Continue
69 : : * handing them one, to make it less painful to adapt FDWs to new
70 : : * versions. The cost of a heap slot over a virtual slot is pretty
71 : : * small.
72 : : */
73 : 222 : tts_cb = &TTSOpsHeapTuple;
74 : : }
75 : : else
76 : : {
77 : : /*
78 : : * These need to be supported, as some parts of the code (like COPY)
79 : : * need to create slots for such relations too. It seems better to
80 : : * centralize the knowledge that a heap slot is the right thing in
81 : : * that case here.
82 : : */
83 [ + + - + ]: 3670 : Assert(relation->rd_rel->relkind == RELKIND_VIEW ||
84 : : relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
85 : 3670 : tts_cb = &TTSOpsVirtual;
86 : : }
87 : :
88 : 14593996 : return tts_cb;
89 : : }
90 : :
91 : : TupleTableSlot *
92 : 13934550 : table_slot_create(Relation relation, List **reglist)
93 : : {
94 : : const TupleTableSlotOps *tts_cb;
95 : : TupleTableSlot *slot;
96 : :
97 : 13934550 : tts_cb = table_slot_callbacks(relation);
98 : 13934550 : slot = MakeSingleTupleTableSlot(RelationGetDescr(relation), tts_cb);
99 : :
100 [ + + ]: 13934550 : if (reglist)
101 : 541475 : *reglist = lappend(*reglist, slot);
102 : :
103 : 13934550 : return slot;
104 : : }
105 : :
106 : :
107 : : /* ----------------------------------------------------------------------------
108 : : * Table scan functions.
109 : : * ----------------------------------------------------------------------------
110 : : */
111 : :
112 : : TableScanDesc
171 alvherre@kurilemu.de 113 :GNC 32995 : table_beginscan_catalog(Relation relation, int nkeys, ScanKeyData *key)
114 : : {
2492 andres@anarazel.de 115 :CBC 32995 : uint32 flags = SO_TYPE_SEQSCAN |
116 : : SO_ALLOW_STRAT | SO_ALLOW_SYNC | SO_ALLOW_PAGEMODE | SO_TEMP_SNAPSHOT;
2561 117 : 32995 : Oid relid = RelationGetRelid(relation);
118 : 32995 : Snapshot snapshot = RegisterSnapshot(GetCatalogSnapshot(relid));
119 : :
45 andres@anarazel.de 120 :GNC 32995 : return table_beginscan_common(relation, snapshot, nkeys, key,
121 : : NULL, flags);
122 : : }
123 : :
124 : :
125 : : /* ----------------------------------------------------------------------------
126 : : * Parallel table scan related functions.
127 : : * ----------------------------------------------------------------------------
128 : : */
129 : :
130 : : Size
2561 andres@anarazel.de 131 :CBC 581 : table_parallelscan_estimate(Relation rel, Snapshot snapshot)
132 : : {
133 : 581 : Size sz = 0;
134 : :
135 [ + + - + ]: 581 : if (IsMVCCSnapshot(snapshot))
136 : 484 : sz = add_size(sz, EstimateSnapshotSpace(snapshot));
137 : : else
138 [ - + ]: 97 : Assert(snapshot == SnapshotAny);
139 : :
140 : 581 : sz = add_size(sz, rel->rd_tableam->parallelscan_estimate(rel));
141 : :
142 : 581 : return sz;
143 : : }
144 : :
145 : : void
146 : 581 : table_parallelscan_initialize(Relation rel, ParallelTableScanDesc pscan,
147 : : Snapshot snapshot)
148 : : {
149 : 581 : Size snapshot_off = rel->rd_tableam->parallelscan_initialize(rel, pscan);
150 : :
151 : 581 : pscan->phs_snapshot_off = snapshot_off;
152 : :
153 [ + + - + ]: 581 : if (IsMVCCSnapshot(snapshot))
154 : : {
155 : 484 : SerializeSnapshot(snapshot, (char *) pscan + pscan->phs_snapshot_off);
156 : 484 : pscan->phs_snapshot_any = false;
157 : : }
158 : : else
159 : : {
160 [ - + ]: 97 : Assert(snapshot == SnapshotAny);
161 : 97 : pscan->phs_snapshot_any = true;
162 : : }
163 : 581 : }
164 : :
165 : : TableScanDesc
1273 pg@bowt.ie 166 : 2068 : table_beginscan_parallel(Relation relation, ParallelTableScanDesc pscan)
167 : : {
168 : : Snapshot snapshot;
2492 andres@anarazel.de 169 : 2068 : uint32 flags = SO_TYPE_SEQSCAN |
170 : : SO_ALLOW_STRAT | SO_ALLOW_SYNC | SO_ALLOW_PAGEMODE;
171 : :
541 tgl@sss.pgh.pa.us 172 [ + - + - : 2068 : Assert(RelFileLocatorEquals(relation->rd_locator, pscan->phs_locator));
- + ]
173 : :
1273 pg@bowt.ie 174 [ + + ]: 2068 : if (!pscan->phs_snapshot_any)
175 : : {
176 : : /* Snapshot was serialized -- restore it */
177 : 1861 : snapshot = RestoreSnapshot((char *) pscan + pscan->phs_snapshot_off);
2561 andres@anarazel.de 178 : 1861 : RegisterSnapshot(snapshot);
2492 179 : 1861 : flags |= SO_TEMP_SNAPSHOT;
180 : : }
181 : : else
182 : : {
183 : : /* SnapshotAny passed by caller (not serialized) */
2561 184 : 207 : snapshot = SnapshotAny;
185 : : }
186 : :
45 andres@anarazel.de 187 :GNC 2068 : return table_beginscan_common(relation, snapshot, 0, NULL,
188 : : pscan, flags);
189 : : }
190 : :
191 : : TableScanDesc
108 drowley@postgresql.o 192 : 60 : table_beginscan_parallel_tidrange(Relation relation,
193 : : ParallelTableScanDesc pscan)
194 : : {
195 : : Snapshot snapshot;
196 : 60 : uint32 flags = SO_TYPE_TIDRANGESCAN | SO_ALLOW_PAGEMODE;
197 : : TableScanDesc sscan;
198 : :
199 [ + - + - : 60 : Assert(RelFileLocatorEquals(relation->rd_locator, pscan->phs_locator));
- + ]
200 : :
201 : : /* disable syncscan in parallel tid range scan. */
202 : 60 : pscan->phs_syncscan = false;
203 : :
204 [ + - ]: 60 : if (!pscan->phs_snapshot_any)
205 : : {
206 : : /* Snapshot was serialized -- restore it */
207 : 60 : snapshot = RestoreSnapshot((char *) pscan + pscan->phs_snapshot_off);
208 : 60 : RegisterSnapshot(snapshot);
209 : 60 : flags |= SO_TEMP_SNAPSHOT;
210 : : }
211 : : else
212 : : {
213 : : /* SnapshotAny passed by caller (not serialized) */
108 drowley@postgresql.o 214 :UNC 0 : snapshot = SnapshotAny;
215 : : }
216 : :
45 andres@anarazel.de 217 :GNC 60 : sscan = table_beginscan_common(relation, snapshot, 0, NULL,
218 : : pscan, flags);
108 drowley@postgresql.o 219 : 60 : return sscan;
220 : : }
221 : :
222 : :
223 : : /* ----------------------------------------------------------------------------
224 : : * Index scan related functions.
225 : : * ----------------------------------------------------------------------------
226 : : */
227 : :
228 : : /*
229 : : * To perform that check simply start an index scan, create the necessary
230 : : * slot, do the heap lookup, and shut everything down again. This could be
231 : : * optimized, but is unlikely to matter from a performance POV. If there
232 : : * frequently are live index pointers also matching a unique index key, the
233 : : * CPU overhead of this routine is unlikely to matter.
234 : : *
235 : : * Note that *tid may be modified when we return true if the AM supports
236 : : * storing multiple row versions reachable via a single index entry (like
237 : : * heap's HOT).
238 : : */
239 : : bool
2547 andres@anarazel.de 240 :CBC 5733472 : table_index_fetch_tuple_check(Relation rel,
241 : : ItemPointer tid,
242 : : Snapshot snapshot,
243 : : bool *all_dead)
244 : : {
245 : : IndexFetchTableData *scan;
246 : : TupleTableSlot *slot;
247 : 5733472 : bool call_again = false;
248 : : bool found;
249 : :
250 : 5733472 : slot = table_slot_create(rel, NULL);
251 : 5733472 : scan = table_index_fetch_begin(rel);
252 : 5733472 : found = table_index_fetch_tuple(scan, tid, snapshot, slot, &call_again,
253 : : all_dead);
254 : 5733472 : table_index_fetch_end(scan);
255 : 5733472 : ExecDropSingleTupleTableSlot(slot);
256 : :
257 : 5733472 : return found;
258 : : }
259 : :
260 : :
261 : : /* ------------------------------------------------------------------------
262 : : * Functions for non-modifying operations on individual tuples
263 : : * ------------------------------------------------------------------------
264 : : */
265 : :
266 : : void
2488 267 : 156 : table_tuple_get_latest_tid(TableScanDesc scan, ItemPointer tid)
268 : : {
2489 tgl@sss.pgh.pa.us 269 : 156 : Relation rel = scan->rs_rd;
2494 andres@anarazel.de 270 : 156 : const TableAmRoutine *tableam = rel->rd_tableam;
271 : :
272 : : /*
273 : : * Since this can be called with user-supplied TID, don't trust the input
274 : : * too much.
275 : : */
276 [ + + ]: 156 : if (!tableam->tuple_tid_valid(scan, tid))
277 [ + - ]: 6 : ereport(ERROR,
278 : : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
279 : : errmsg("tid (%u, %u) is not valid for relation \"%s\"",
280 : : ItemPointerGetBlockNumberNoCheck(tid),
281 : : ItemPointerGetOffsetNumberNoCheck(tid),
282 : : RelationGetRelationName(rel))));
283 : :
2493 tgl@sss.pgh.pa.us 284 : 150 : tableam->tuple_get_latest_tid(scan, tid);
2494 andres@anarazel.de 285 : 150 : }
286 : :
287 : :
288 : : /* ----------------------------------------------------------------------------
289 : : * Functions to make modifications a bit simpler.
290 : : * ----------------------------------------------------------------------------
291 : : */
292 : :
293 : : /*
294 : : * simple_table_tuple_insert - insert a tuple
295 : : *
296 : : * Currently, this routine differs from table_tuple_insert only in supplying a
297 : : * default command ID and not allowing access to the speedup options.
298 : : */
299 : : void
703 akorotkov@postgresql 300 : 76013 : simple_table_tuple_insert(Relation rel, TupleTableSlot *slot)
301 : : {
302 : 76013 : table_tuple_insert(rel, slot, GetCurrentCommandId(true), 0, NULL);
2549 andres@anarazel.de 303 : 76013 : }
304 : :
305 : : /*
306 : : * simple_table_tuple_delete - delete a tuple
307 : : *
308 : : * This routine may be used to delete a tuple when concurrent updates of
309 : : * the target tuple are not expected (for example, because we have a lock
310 : : * on the relation associated with the tuple). Any failure is reported
311 : : * via ereport().
312 : : */
313 : : void
703 akorotkov@postgresql 314 : 40313 : simple_table_tuple_delete(Relation rel, ItemPointer tid, Snapshot snapshot)
315 : : {
316 : : TM_Result result;
317 : : TM_FailureData tmfd;
318 : :
2488 andres@anarazel.de 319 : 40313 : result = table_tuple_delete(rel, tid,
320 : : GetCurrentCommandId(true),
321 : : snapshot, InvalidSnapshot,
322 : : true /* wait for commit */ ,
323 : : &tmfd, false /* changingPart */ );
324 : :
2549 325 [ - + - - : 40313 : switch (result)
- ]
326 : : {
2549 andres@anarazel.de 327 :UBC 0 : case TM_SelfModified:
328 : : /* Tuple was already updated in current command? */
329 [ # # ]: 0 : elog(ERROR, "tuple already updated by self");
330 : : break;
331 : :
2549 andres@anarazel.de 332 :CBC 40313 : case TM_Ok:
333 : : /* done successfully */
334 : 40313 : break;
335 : :
2549 andres@anarazel.de 336 :UBC 0 : case TM_Updated:
337 [ # # ]: 0 : elog(ERROR, "tuple concurrently updated");
338 : : break;
339 : :
340 : 0 : case TM_Deleted:
341 [ # # ]: 0 : elog(ERROR, "tuple concurrently deleted");
342 : : break;
343 : :
344 : 0 : default:
2488 345 [ # # ]: 0 : elog(ERROR, "unrecognized table_tuple_delete status: %u", result);
346 : : break;
347 : : }
2549 andres@anarazel.de 348 :CBC 40313 : }
349 : :
350 : : /*
351 : : * simple_table_tuple_update - replace a tuple
352 : : *
353 : : * This routine may be used to update a tuple when concurrent updates of
354 : : * the target tuple are not expected (for example, because we have a lock
355 : : * on the relation associated with the tuple). Any failure is reported
356 : : * via ereport().
357 : : */
358 : : void
2488 359 : 31919 : simple_table_tuple_update(Relation rel, ItemPointer otid,
360 : : TupleTableSlot *slot,
361 : : Snapshot snapshot,
362 : : TU_UpdateIndexes *update_indexes)
363 : : {
364 : : TM_Result result;
365 : : TM_FailureData tmfd;
366 : : LockTupleMode lockmode;
367 : :
368 : 31919 : result = table_tuple_update(rel, otid, slot,
369 : : GetCurrentCommandId(true),
370 : : snapshot, InvalidSnapshot,
371 : : true /* wait for commit */ ,
372 : : &tmfd, &lockmode, update_indexes);
373 : :
2549 374 [ - + - - : 31919 : switch (result)
- ]
375 : : {
2549 andres@anarazel.de 376 :UBC 0 : case TM_SelfModified:
377 : : /* Tuple was already updated in current command? */
378 [ # # ]: 0 : elog(ERROR, "tuple already updated by self");
379 : : break;
380 : :
2549 andres@anarazel.de 381 :CBC 31919 : case TM_Ok:
382 : : /* done successfully */
383 : 31919 : break;
384 : :
2549 andres@anarazel.de 385 :UBC 0 : case TM_Updated:
386 [ # # ]: 0 : elog(ERROR, "tuple concurrently updated");
387 : : break;
388 : :
389 : 0 : case TM_Deleted:
390 [ # # ]: 0 : elog(ERROR, "tuple concurrently deleted");
391 : : break;
392 : :
393 : 0 : default:
2488 394 [ # # ]: 0 : elog(ERROR, "unrecognized table_tuple_update status: %u", result);
395 : : break;
396 : : }
2549 andres@anarazel.de 397 :CBC 31919 : }
398 : :
399 : :
400 : : /* ----------------------------------------------------------------------------
401 : : * Helper functions to implement parallel scans for block oriented AMs.
402 : : * ----------------------------------------------------------------------------
403 : : */
404 : :
405 : : Size
2561 406 : 581 : table_block_parallelscan_estimate(Relation rel)
407 : : {
408 : 581 : return sizeof(ParallelBlockTableScanDescData);
409 : : }
410 : :
411 : : Size
412 : 581 : table_block_parallelscan_initialize(Relation rel, ParallelTableScanDesc pscan)
413 : : {
414 : 581 : ParallelBlockTableScanDesc bpscan = (ParallelBlockTableScanDesc) pscan;
415 : :
541 tgl@sss.pgh.pa.us 416 : 581 : bpscan->base.phs_locator = rel->rd_locator;
2561 andres@anarazel.de 417 : 581 : bpscan->phs_nblocks = RelationGetNumberOfBlocks(rel);
418 : : /* compare phs_syncscan initialization to similar logic in initscan */
419 : 1555 : bpscan->base.phs_syncscan = synchronize_seqscans &&
420 [ + + + - ]: 974 : !RelationUsesLocalBuffers(rel) &&
421 [ + + ]: 393 : bpscan->phs_nblocks > NBuffers / 4;
422 : 581 : SpinLockInit(&bpscan->phs_mutex);
423 : 581 : bpscan->phs_startblock = InvalidBlockNumber;
108 drowley@postgresql.o 424 :GNC 581 : bpscan->phs_numblock = InvalidBlockNumber;
2561 andres@anarazel.de 425 :CBC 581 : pg_atomic_init_u64(&bpscan->phs_nallocated, 0);
426 : :
427 : 581 : return sizeof(ParallelBlockTableScanDescData);
428 : : }
429 : :
430 : : void
431 : 114 : table_block_parallelscan_reinitialize(Relation rel, ParallelTableScanDesc pscan)
432 : : {
433 : 114 : ParallelBlockTableScanDesc bpscan = (ParallelBlockTableScanDesc) pscan;
434 : :
435 : 114 : pg_atomic_write_u64(&bpscan->phs_nallocated, 0);
436 : 114 : }
437 : :
438 : : /*
439 : : * find and set the scan's startblock
440 : : *
441 : : * Determine where the parallel seq scan should start. This function may be
442 : : * called many times, once by each parallel worker. We must be careful only
443 : : * to set the phs_startblock and phs_numblock fields once.
444 : : *
445 : : * Callers may optionally specify a non-InvalidBlockNumber value for
446 : : * 'startblock' to force the scan to start at the given page. Likewise,
447 : : * 'numblocks' can be specified as a non-InvalidBlockNumber to limit the
448 : : * number of blocks to scan to that many blocks.
449 : : */
450 : : void
2058 drowley@postgresql.o 451 : 1712 : table_block_parallelscan_startblock_init(Relation rel,
452 : : ParallelBlockTableScanWorker pbscanwork,
453 : : ParallelBlockTableScanDesc pbscan,
454 : : BlockNumber startblock,
455 : : BlockNumber numblocks)
456 : : {
457 : : StaticAssertDecl(MaxBlockNumber <= 0xFFFFFFFE,
458 : : "pg_nextpower2_32 may be too small for non-standard BlockNumber width");
459 : :
2561 andres@anarazel.de 460 : 1712 : BlockNumber sync_startpage = InvalidBlockNumber;
461 : : BlockNumber scan_nblocks;
462 : :
463 : : /* Reset the state we use for controlling allocation size. */
2058 drowley@postgresql.o 464 : 1712 : memset(pbscanwork, 0, sizeof(*pbscanwork));
465 : :
2561 andres@anarazel.de 466 : 1713 : retry:
467 : : /* Grab the spinlock. */
468 [ + + ]: 1713 : SpinLockAcquire(&pbscan->phs_mutex);
469 : :
470 : : /*
471 : : * When the caller specified a limit on the number of blocks to scan, set
472 : : * that in the ParallelBlockTableScanDesc, if it's not been done by
473 : : * another worker already.
474 : : */
108 drowley@postgresql.o 475 [ + + ]:GNC 1713 : if (numblocks != InvalidBlockNumber &&
476 [ + + ]: 60 : pbscan->phs_numblock == InvalidBlockNumber)
477 : : {
478 : 12 : pbscan->phs_numblock = numblocks;
479 : : }
480 : :
481 : : /*
482 : : * If the scan's phs_startblock has not yet been initialized, we must do
483 : : * so now. If a startblock was specified, start there, otherwise if this
484 : : * is not a synchronized scan, we just start at block 0, but if it is a
485 : : * synchronized scan, we must get the starting position from the
486 : : * synchronized scan machinery. We can't hold the spinlock while doing
487 : : * that, though, so release the spinlock, get the information we need, and
488 : : * retry. If nobody else has initialized the scan in the meantime, we'll
489 : : * fill in the value we fetched on the second time through.
490 : : */
2561 andres@anarazel.de 491 [ + + ]:CBC 1713 : if (pbscan->phs_startblock == InvalidBlockNumber)
492 : : {
108 drowley@postgresql.o 493 [ + + ]:GNC 572 : if (startblock != InvalidBlockNumber)
494 : 12 : pbscan->phs_startblock = startblock;
495 [ + + ]: 560 : else if (!pbscan->base.phs_syncscan)
2561 andres@anarazel.de 496 :CBC 558 : pbscan->phs_startblock = 0;
497 [ + + ]: 2 : else if (sync_startpage != InvalidBlockNumber)
498 : 1 : pbscan->phs_startblock = sync_startpage;
499 : : else
500 : : {
501 : 1 : SpinLockRelease(&pbscan->phs_mutex);
502 : 1 : sync_startpage = ss_get_location(rel, pbscan->phs_nblocks);
503 : 1 : goto retry;
504 : : }
505 : : }
506 : 1712 : SpinLockRelease(&pbscan->phs_mutex);
507 : :
508 : : /*
509 : : * Figure out how many blocks we're going to scan; either all of them, or
510 : : * just phs_numblock's worth, if a limit has been imposed.
511 : : */
108 drowley@postgresql.o 512 [ + + ]:GNC 1712 : if (pbscan->phs_numblock == InvalidBlockNumber)
513 : 1652 : scan_nblocks = pbscan->phs_nblocks;
514 : : else
515 : 60 : scan_nblocks = pbscan->phs_numblock;
516 : :
517 : : /*
518 : : * We determine the chunk size based on scan_nblocks. First we split
519 : : * scan_nblocks into PARALLEL_SEQSCAN_NCHUNKS chunks then we calculate the
520 : : * next highest power of 2 number of the result. This means we split the
521 : : * blocks we're scanning into somewhere between PARALLEL_SEQSCAN_NCHUNKS
522 : : * and PARALLEL_SEQSCAN_NCHUNKS / 2 chunks.
523 : : */
524 [ + + ]: 1712 : pbscanwork->phsw_chunk_size = pg_nextpower2_32(Max(scan_nblocks /
525 : : PARALLEL_SEQSCAN_NCHUNKS, 1));
526 : :
527 : : /*
528 : : * Ensure we don't go over the maximum chunk size with larger tables. This
529 : : * means we may get much more than PARALLEL_SEQSCAN_NCHUNKS for larger
530 : : * tables. Too large a chunk size has been shown to be detrimental to
531 : : * sequential scan performance.
532 : : */
533 : 1712 : pbscanwork->phsw_chunk_size = Min(pbscanwork->phsw_chunk_size,
534 : : PARALLEL_SEQSCAN_MAX_CHUNK_SIZE);
2561 andres@anarazel.de 535 :CBC 1712 : }
536 : :
537 : : /*
538 : : * get the next page to scan
539 : : *
540 : : * Get the next page to scan. Even if there are no pages left to scan,
541 : : * another backend could have grabbed a page to scan and not yet finished
542 : : * looking at it, so it doesn't follow that the scan is done when the first
543 : : * backend gets an InvalidBlockNumber return.
544 : : */
545 : : BlockNumber
2058 drowley@postgresql.o 546 : 101777 : table_block_parallelscan_nextpage(Relation rel,
547 : : ParallelBlockTableScanWorker pbscanwork,
548 : : ParallelBlockTableScanDesc pbscan)
549 : : {
550 : : BlockNumber scan_nblocks;
551 : : BlockNumber page;
552 : : uint64 nallocated;
553 : :
554 : : /*
555 : : * The logic below allocates block numbers out to parallel workers in a
556 : : * way that each worker will receive a set of consecutive block numbers to
557 : : * scan. Earlier versions of this would allocate the next highest block
558 : : * number to the next worker to call this function. This would generally
559 : : * result in workers never receiving consecutive block numbers. Some
560 : : * operating systems would not detect the sequential I/O pattern due to
561 : : * each backend being a different process which could result in poor
562 : : * performance due to inefficient or no readahead. To work around this
563 : : * issue, we now allocate a range of block numbers for each worker and
564 : : * when they come back for another block, we give them the next one in
565 : : * that range until the range is complete. When the worker completes the
566 : : * range of blocks we then allocate another range for it and return the
567 : : * first block number from that range.
568 : : *
569 : : * Here we name these ranges of blocks "chunks". The initial size of
570 : : * these chunks is determined in table_block_parallelscan_startblock_init
571 : : * based on the number of blocks to scan. Towards the end of the scan, we
572 : : * start making reductions in the size of the chunks in order to attempt
573 : : * to divide the remaining work over all the workers as evenly as
574 : : * possible.
575 : : *
576 : : * Here pbscanwork is local worker memory. phsw_chunk_remaining tracks
577 : : * the number of blocks remaining in the chunk. When that reaches 0 then
578 : : * we must allocate a new chunk for the worker.
579 : : *
580 : : * phs_nallocated tracks how many blocks have been allocated to workers
581 : : * already. When phs_nallocated >= rs_nblocks, all blocks have been
582 : : * allocated.
583 : : *
584 : : * Because we use an atomic fetch-and-add to fetch the current value, the
585 : : * phs_nallocated counter will exceed rs_nblocks, because workers will
586 : : * still increment the value, when they try to allocate the next block but
587 : : * all blocks have been allocated already. The counter must be 64 bits
588 : : * wide because of that, to avoid wrapping around when scan_nblocks is
589 : : * close to 2^32.
590 : : *
591 : : * The actual block to return is calculated by adding the counter to the
592 : : * starting block number, modulo phs_nblocks.
593 : : */
594 : :
595 : : /* First, figure out how many blocks we're planning on scanning */
108 drowley@postgresql.o 596 [ + + ]:GNC 101777 : if (pbscan->phs_numblock == InvalidBlockNumber)
597 : 101468 : scan_nblocks = pbscan->phs_nblocks;
598 : : else
599 : 309 : scan_nblocks = pbscan->phs_numblock;
600 : :
601 : : /*
602 : : * Now check if we have any remaining blocks in a previous chunk for this
603 : : * worker. We must consume all of the blocks from that before we allocate
604 : : * a new chunk to the worker.
605 : : */
2058 drowley@postgresql.o 606 [ + + ]:CBC 101777 : if (pbscanwork->phsw_chunk_remaining > 0)
607 : : {
608 : : /*
609 : : * Give them the next block in the range and update the remaining
610 : : * number of blocks.
611 : : */
612 : 6513 : nallocated = ++pbscanwork->phsw_nallocated;
613 : 6513 : pbscanwork->phsw_chunk_remaining--;
614 : : }
615 : : else
616 : : {
617 : : /*
618 : : * When we've only got PARALLEL_SEQSCAN_RAMPDOWN_CHUNKS chunks
619 : : * remaining in the scan, we half the chunk size. Since we reduce the
620 : : * chunk size here, we'll hit this again after doing
621 : : * PARALLEL_SEQSCAN_RAMPDOWN_CHUNKS at the new size. After a few
622 : : * iterations of this, we'll end up doing the last few blocks with the
623 : : * chunk size set to 1.
624 : : */
625 [ + + ]: 95264 : if (pbscanwork->phsw_chunk_size > 1 &&
108 drowley@postgresql.o 626 :GNC 2215 : pbscanwork->phsw_nallocated > scan_nblocks -
2058 drowley@postgresql.o 627 [ + + ]:CBC 2215 : (pbscanwork->phsw_chunk_size * PARALLEL_SEQSCAN_RAMPDOWN_CHUNKS))
628 : 4 : pbscanwork->phsw_chunk_size >>= 1;
629 : :
630 : 95264 : nallocated = pbscanwork->phsw_nallocated =
631 : 95264 : pg_atomic_fetch_add_u64(&pbscan->phs_nallocated,
632 : 95264 : pbscanwork->phsw_chunk_size);
633 : :
634 : : /*
635 : : * Set the remaining number of blocks in this chunk so that subsequent
636 : : * calls from this worker continue on with this chunk until it's done.
637 : : */
638 : 95264 : pbscanwork->phsw_chunk_remaining = pbscanwork->phsw_chunk_size - 1;
639 : : }
640 : :
641 : : /* Check if we've run out of blocks to scan */
108 drowley@postgresql.o 642 [ + + ]:GNC 101777 : if (nallocated >= scan_nblocks)
2561 andres@anarazel.de 643 :CBC 1712 : page = InvalidBlockNumber; /* all blocks have been allocated */
644 : : else
645 : 100065 : page = (nallocated + pbscan->phs_startblock) % pbscan->phs_nblocks;
646 : :
647 : : /*
648 : : * Report scan location. Normally, we report the current page number.
649 : : * When we reach the end of the scan, though, we report the starting page,
650 : : * not the ending page, just so the starting positions for later scans
651 : : * doesn't slew backwards. We only report the position at the end of the
652 : : * scan once, though: subsequent callers will report nothing.
653 : : */
654 [ + + ]: 101777 : if (pbscan->base.phs_syncscan)
655 : : {
656 [ + + ]: 8852 : if (page != InvalidBlockNumber)
657 : 8850 : ss_report_location(rel, page);
658 [ + + ]: 2 : else if (nallocated == pbscan->phs_nblocks)
659 : 1 : ss_report_location(rel, pbscan->phs_startblock);
660 : : }
661 : :
662 : 101777 : return page;
663 : : }
664 : :
665 : : /* ----------------------------------------------------------------------------
666 : : * Helper functions to implement relation sizing for block oriented AMs.
667 : : * ----------------------------------------------------------------------------
668 : : */
669 : :
670 : : /*
671 : : * table_block_relation_size
672 : : *
673 : : * If a table AM uses the various relation forks as the sole place where data
674 : : * is stored, and if it uses them in the expected manner (e.g. the actual data
675 : : * is in the main fork rather than some other), it can use this implementation
676 : : * of the relation_size callback rather than implementing its own.
677 : : */
678 : : uint64
2442 rhaas@postgresql.org 679 : 1903172 : table_block_relation_size(Relation rel, ForkNumber forkNumber)
680 : : {
681 : 1903172 : uint64 nblocks = 0;
682 : :
683 : : /* InvalidForkNumber indicates returning the size for all forks */
684 [ - + ]: 1903172 : if (forkNumber == InvalidForkNumber)
685 : : {
2442 rhaas@postgresql.org 686 [ # # ]:UBC 0 : for (int i = 0; i < MAX_FORKNUM; i++)
1707 tgl@sss.pgh.pa.us 687 : 0 : nblocks += smgrnblocks(RelationGetSmgr(rel), i);
688 : : }
689 : : else
1707 tgl@sss.pgh.pa.us 690 :CBC 1903172 : nblocks = smgrnblocks(RelationGetSmgr(rel), forkNumber);
691 : :
2442 rhaas@postgresql.org 692 : 1903153 : return nblocks * BLCKSZ;
693 : : }
694 : :
695 : : /*
696 : : * table_block_relation_estimate_size
697 : : *
698 : : * This function can't be directly used as the implementation of the
699 : : * relation_estimate_size callback, because it has a few additional parameters.
700 : : * Instead, it is intended to be used as a helper function; the caller can
701 : : * pass through the arguments to its relation_estimate_size function plus the
702 : : * additional values required here.
703 : : *
704 : : * overhead_bytes_per_tuple should contain the approximate number of bytes
705 : : * of storage required to store a tuple above and beyond what is required for
706 : : * the tuple data proper. Typically, this would include things like the
707 : : * size of the tuple header and item pointer. This is only used for query
708 : : * planning, so a table AM where the value is not constant could choose to
709 : : * pass a "best guess".
710 : : *
711 : : * usable_bytes_per_page should contain the approximate number of bytes per
712 : : * page usable for tuple data, excluding the page header and any anticipated
713 : : * special space.
714 : : */
715 : : void
716 : 253399 : table_block_relation_estimate_size(Relation rel, int32 *attr_widths,
717 : : BlockNumber *pages, double *tuples,
718 : : double *allvisfrac,
719 : : Size overhead_bytes_per_tuple,
720 : : Size usable_bytes_per_page)
721 : : {
722 : : BlockNumber curpages;
723 : : BlockNumber relpages;
724 : : double reltuples;
725 : : BlockNumber relallvisible;
726 : : double density;
727 : :
728 : : /* it should have storage, so we can call the smgr */
729 : 253399 : curpages = RelationGetNumberOfBlocks(rel);
730 : :
731 : : /* coerce values in pg_class to more desirable types */
732 : 253399 : relpages = (BlockNumber) rel->rd_rel->relpages;
733 : 253399 : reltuples = (double) rel->rd_rel->reltuples;
734 : 253399 : relallvisible = (BlockNumber) rel->rd_rel->relallvisible;
735 : :
736 : : /*
737 : : * HACK: if the relation has never yet been vacuumed, use a minimum size
738 : : * estimate of 10 pages. The idea here is to avoid assuming a
739 : : * newly-created table is really small, even if it currently is, because
740 : : * that may not be true once some data gets loaded into it. Once a vacuum
741 : : * or analyze cycle has been done on it, it's more reasonable to believe
742 : : * the size is somewhat stable.
743 : : *
744 : : * (Note that this is only an issue if the plan gets cached and used again
745 : : * after the table has been filled. What we're trying to avoid is using a
746 : : * nestloop-type plan on a table that has grown substantially since the
747 : : * plan was made. Normally, autovacuum/autoanalyze will occur once enough
748 : : * inserts have happened and cause cached-plan invalidation; but that
749 : : * doesn't happen instantaneously, and it won't happen at all for cases
750 : : * such as temporary tables.)
751 : : *
752 : : * We test "never vacuumed" by seeing whether reltuples < 0.
753 : : *
754 : : * If the table has inheritance children, we don't apply this heuristic.
755 : : * Totally empty parent tables are quite common, so we should be willing
756 : : * to believe that they are empty.
757 : : */
758 [ + + + + ]: 253399 : if (curpages < 10 &&
2023 tgl@sss.pgh.pa.us 759 : 59352 : reltuples < 0 &&
2442 rhaas@postgresql.org 760 [ + + ]: 59352 : !rel->rd_rel->relhassubclass)
761 : 58027 : curpages = 10;
762 : :
763 : : /* report estimated # pages */
764 : 253399 : *pages = curpages;
765 : : /* quick exit if rel is clearly empty */
766 [ + + ]: 253399 : if (curpages == 0)
767 : : {
768 : 16115 : *tuples = 0;
769 : 16115 : *allvisfrac = 0;
770 : 16115 : return;
771 : : }
772 : :
773 : : /* estimate number of tuples from previous tuple density */
2023 tgl@sss.pgh.pa.us 774 [ + + + + ]: 237284 : if (reltuples >= 0 && relpages > 0)
2442 rhaas@postgresql.org 775 : 154846 : density = reltuples / (double) relpages;
776 : : else
777 : : {
778 : : /*
779 : : * When we have no data because the relation was never yet vacuumed,
780 : : * estimate tuple width from attribute datatypes. We assume here that
781 : : * the pages are completely full, which is OK for tables but is
782 : : * probably an overestimate for indexes. Fortunately
783 : : * get_relation_info() can clamp the overestimate to the parent
784 : : * table's size.
785 : : *
786 : : * Note: this code intentionally disregards alignment considerations,
787 : : * because (a) that would be gilding the lily considering how crude
788 : : * the estimate is, (b) it creates platform dependencies in the
789 : : * default plans which are kind of a headache for regression testing,
790 : : * and (c) different table AMs might use different padding schemes.
791 : : */
792 : : int32 tuple_width;
793 : : int fillfactor;
794 : :
795 : : /*
796 : : * Without reltuples/relpages, we also need to consider fillfactor.
797 : : * The other branch considers it implicitly by calculating density
798 : : * from actual relpages/reltuples statistics.
799 : : */
703 akorotkov@postgresql 800 [ + + ]: 82438 : fillfactor = RelationGetFillFactor(rel, HEAP_DEFAULT_FILLFACTOR);
801 : :
2442 rhaas@postgresql.org 802 : 82438 : tuple_width = get_rel_data_width(rel, attr_widths);
803 : 82438 : tuple_width += overhead_bytes_per_tuple;
804 : : /* note: integer division is intentional here */
986 tomas.vondra@postgre 805 : 82438 : density = (usable_bytes_per_page * fillfactor / 100) / tuple_width;
806 : : /* There's at least one row on the page, even with low fillfactor. */
389 807 : 82438 : density = clamp_row_est(density);
808 : : }
2442 rhaas@postgresql.org 809 : 237284 : *tuples = rint(density * (double) curpages);
810 : :
811 : : /*
812 : : * We use relallvisible as-is, rather than scaling it up like we do for
813 : : * the pages and tuples counts, on the theory that any pages added since
814 : : * the last VACUUM are most likely not marked all-visible. But costsize.c
815 : : * wants it converted to a fraction.
816 : : */
817 [ + + - + ]: 237284 : if (relallvisible == 0 || curpages <= 0)
818 : 112262 : *allvisfrac = 0;
819 [ + + ]: 125022 : else if ((double) relallvisible >= curpages)
820 : 73639 : *allvisfrac = 1;
821 : : else
822 : 51383 : *allvisfrac = (double) relallvisible / curpages;
823 : : }
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