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Commit33d3ad4

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Code review for patch to avoid second scan when vacuuming index-less
table: avoid invoking LockBufferForCleanup without need, put out thesame log message we would have before, minor code beautification.
1 parentea21eea commit33d3ad4

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1 file changed

+53
-32
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1 file changed

+53
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‎src/backend/commands/vacuumlazy.c‎

Lines changed: 53 additions & 32 deletions
Original file line numberDiff line numberDiff line change
@@ -16,10 +16,6 @@
1616
* perform a pass of index cleanup and page compaction, then resume the heap
1717
* scan with an empty TID array.
1818
*
19-
* As a special exception if we're processing a table with no indexes we can
20-
* vacuum each page as we go so we don't need to allocate more space than
21-
* enough to hold as many heap tuples fit on one page.
22-
*
2319
* We can limit the storage for page free space to MaxFSMPages entries,
2420
* since that's the most the free space map will be willing to remember
2521
* anyway.If the relation has fewer than that many pages with free space,
@@ -29,13 +25,18 @@
2925
* have more than MaxFSMPages entries in all. The surviving page entries
3026
* are passed to the free space map at conclusion of the scan.
3127
*
28+
* If we're processing a table with no indexes, we can just vacuum each page
29+
* as we go; there's no need to save up multiple tuples to minimize the number
30+
* of index scans performed. So we don't use maintenance_work_mem memory for
31+
* the TID array, just enough to hold as many heap tuples as fit on one page.
32+
*
3233
*
3334
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
3435
* Portions Copyright (c) 1994, Regents of the University of California
3536
*
3637
*
3738
* IDENTIFICATION
38-
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.77 2006/09/04 21:40:23 momjian Exp $
39+
* $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.78 2006/09/13 17:47:08 tgl Exp $
3940
*
4041
*-------------------------------------------------------------------------
4142
*/
@@ -68,6 +69,8 @@
6869

6970
typedefstructLVRelStats
7071
{
72+
/* hasindex = true means two-pass strategy; false means one-pass */
73+
boolhasindex;
7174
/* Overall statistics about rel */
7275
BlockNumberrel_pages;
7376
doublerel_tuples;
@@ -110,7 +113,7 @@ static void lazy_truncate_heap(Relation onerel, LVRelStats *vacrelstats,
110113
TransactionIdOldestXmin);
111114
staticBlockNumbercount_nondeletable_pages(Relationonerel,
112115
LVRelStats*vacrelstats,TransactionIdOldestXmin);
113-
staticvoidlazy_space_alloc(LVRelStats*vacrelstats,BlockNumberrelblocks,unsignednindexes);
116+
staticvoidlazy_space_alloc(LVRelStats*vacrelstats,BlockNumberrelblocks);
114117
staticvoidlazy_record_dead_tuple(LVRelStats*vacrelstats,
115118
ItemPointeritemptr);
116119
staticvoidlazy_record_free_space(LVRelStats*vacrelstats,
@@ -137,7 +140,6 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
137140
LVRelStats*vacrelstats;
138141
Relation*Irel;
139142
intnindexes;
140-
boolhasindex;
141143
BlockNumberpossibly_freeable;
142144
TransactionIdOldestXmin,
143145
FreezeLimit;
@@ -169,7 +171,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
169171

170172
/* Open all indexes of the relation */
171173
vac_open_indexes(onerel,RowExclusiveLock,&nindexes,&Irel);
172-
hasindex= (nindexes>0);
174+
vacrelstats->hasindex= (nindexes>0);
173175

174176
/* Do the vacuuming */
175177
lazy_scan_heap(onerel,vacrelstats,Irel,nindexes,FreezeLimit,OldestXmin);
@@ -195,7 +197,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
195197
vac_update_relstats(RelationGetRelid(onerel),
196198
vacrelstats->rel_pages,
197199
vacrelstats->rel_tuples,
198-
hasindex,
200+
vacrelstats->hasindex,
199201
vacrelstats->minxid,OldestXmin);
200202

201203
/* report results to the stats collector, too */
@@ -210,11 +212,13 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
210212
*This routine sets commit status bits, builds lists of dead tuples
211213
*and pages with free space, and calculates statistics on the number
212214
*of live tuples in the heap. When done, or when we run low on space
213-
*for dead-tuple TIDs, or after every page if the table has no indexes
214-
*invoke vacuuming of indexes and heap.
215+
*for dead-tuple TIDs, invoke vacuuming of indexes and heap.
215216
*
216217
*It also updates the minimum Xid found anywhere on the table in
217218
*vacrelstats->minxid, for later storing it in pg_class.relminxid.
219+
*
220+
*If there are no indexes then we just vacuum each dirty page as we
221+
*process it, since there's no point in gathering many tuples.
218222
*/
219223
staticvoid
220224
lazy_scan_heap(Relationonerel,LVRelStats*vacrelstats,
@@ -225,7 +229,8 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
225229
blkno;
226230
HeapTupleDatatuple;
227231
char*relname;
228-
BlockNumberempty_pages;
232+
BlockNumberempty_pages,
233+
vacuumed_pages;
229234
doublenum_tuples,
230235
tups_vacuumed,
231236
nkeep,
@@ -242,7 +247,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
242247
get_namespace_name(RelationGetNamespace(onerel)),
243248
relname)));
244249

245-
empty_pages=0;
250+
empty_pages=vacuumed_pages=0;
246251
num_tuples=tups_vacuumed=nkeep=nunused=0;
247252

248253
indstats= (IndexBulkDeleteResult**)
@@ -252,7 +257,7 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
252257
vacrelstats->rel_pages=nblocks;
253258
vacrelstats->nonempty_pages=0;
254259

255-
lazy_space_alloc(vacrelstats,nblocks,nindexes);
260+
lazy_space_alloc(vacrelstats,nblocks);
256261

257262
for (blkno=0;blkno<nblocks;blkno++)
258263
{
@@ -287,14 +292,8 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
287292

288293
buf=ReadBuffer(onerel,blkno);
289294

290-
/* In this phase we only need shared access to the buffer unless we're
291-
* going to do the vacuuming now which we do if there are no indexes
292-
*/
293-
294-
if (nindexes)
295-
LockBuffer(buf,BUFFER_LOCK_SHARE);
296-
else
297-
LockBufferForCleanup(buf);
295+
/* In this phase we only need shared access to the buffer */
296+
LockBuffer(buf,BUFFER_LOCK_SHARE);
298297

299298
page=BufferGetPage(buf);
300299

@@ -451,22 +450,34 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
451450
}
452451
}/* scan along page */
453452

453+
/*
454+
* If there are no indexes then we can vacuum the page right now
455+
* instead of doing a second scan.
456+
*/
457+
if (nindexes==0&&
458+
vacrelstats->num_dead_tuples>0)
459+
{
460+
/* Trade in buffer share lock for super-exclusive lock */
461+
LockBuffer(buf,BUFFER_LOCK_UNLOCK);
462+
LockBufferForCleanup(buf);
463+
/* Remove tuples from heap */
464+
lazy_vacuum_page(onerel,blkno,buf,0,vacrelstats);
465+
/* Forget the now-vacuumed tuples, and press on */
466+
vacrelstats->num_dead_tuples=0;
467+
vacuumed_pages++;
468+
}
469+
454470
/*
455471
* If we remembered any tuples for deletion, then the page will be
456472
* visited again by lazy_vacuum_heap, which will compute and record
457473
* its post-compaction free space.If not, then we're done with this
458-
* page, so remember its free space as-is.
474+
* page, so remember its free space as-is. (This path will always
475+
* be taken if there are no indexes.)
459476
*/
460477
if (vacrelstats->num_dead_tuples==prev_dead_count)
461478
{
462479
lazy_record_free_space(vacrelstats,blkno,
463480
PageGetFreeSpace(page));
464-
}elseif (!nindexes) {
465-
/* If there are no indexes we can vacuum the page right now instead
466-
* of doing a second scan */
467-
lazy_vacuum_page(onerel,blkno,buf,0,vacrelstats);
468-
lazy_record_free_space(vacrelstats,blkno,PageGetFreeSpace(BufferGetPage(buf)));
469-
vacrelstats->num_dead_tuples=0;
470481
}
471482

472483
/* Remember the location of the last page with nonremovable tuples */
@@ -499,6 +510,13 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats,
499510
for (i=0;i<nindexes;i++)
500511
lazy_cleanup_index(Irel[i],indstats[i],vacrelstats);
501512

513+
/* If no indexes, make log report that lazy_vacuum_heap would've made */
514+
if (vacuumed_pages)
515+
ereport(elevel,
516+
(errmsg("\"%s\": removed %.0f row versions in %u pages",
517+
RelationGetRelationName(onerel),
518+
tups_vacuumed,vacuumed_pages)));
519+
502520
ereport(elevel,
503521
(errmsg("\"%s\": found %.0f removable, %.0f nonremovable row versions in %u pages",
504522
RelationGetRelationName(onerel),
@@ -908,18 +926,21 @@ count_nondeletable_pages(Relation onerel, LVRelStats *vacrelstats,
908926
* See the comments at the head of this file for rationale.
909927
*/
910928
staticvoid
911-
lazy_space_alloc(LVRelStats*vacrelstats,BlockNumberrelblocks,unsignednindexes)
929+
lazy_space_alloc(LVRelStats*vacrelstats,BlockNumberrelblocks)
912930
{
913931
longmaxtuples;
914932
intmaxpages;
915933

916-
if (nindexes) {
934+
if (vacrelstats->hasindex)
935+
{
917936
maxtuples= (maintenance_work_mem*1024L) /sizeof(ItemPointerData);
918937
maxtuples=Min(maxtuples,INT_MAX);
919938
maxtuples=Min(maxtuples,MaxAllocSize /sizeof(ItemPointerData));
920939
/* stay sane if small maintenance_work_mem */
921940
maxtuples=Max(maxtuples,MaxHeapTuplesPerPage);
922-
}else {
941+
}
942+
else
943+
{
923944
maxtuples=MaxHeapTuplesPerPage;
924945
}
925946

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