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Commitfb5344c

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Use full 64-bit XID for checking if a deleted GiST page is old enough.
Otherwise, after a deleted page gets even older, it becomes unrecyclableagain. B-tree has the same problem, and has had since time immemorial,but let's at least fix this in GiST, where this is new.Backpatch to v12, where GiST page deletion was introduced.Reviewed-by: Andrey BorodinDiscussion:https://www.postgresql.org/message-id/835A15A5-F1B4-4446-A711-BF48357EB602%40yandex-team.ru
1 parente2e992c commitfb5344c

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9 files changed

+134
-28
lines changed

9 files changed

+134
-28
lines changed

‎src/backend/access/gist/gistutil.c

Lines changed: 21 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -882,9 +882,27 @@ gistNewBuffer(Relation r)
882882
bool
883883
gistPageRecyclable(Pagepage)
884884
{
885-
returnPageIsNew(page)||
886-
(GistPageIsDeleted(page)&&
887-
TransactionIdPrecedes(GistPageGetDeleteXid(page),RecentGlobalXmin));
885+
if (PageIsNew(page))
886+
return true;
887+
if (GistPageIsDeleted(page))
888+
{
889+
/*
890+
* The page was deleted, but when? If it was just deleted, a scan
891+
* might have seen the downlink to it, and will read the page later.
892+
* As long as that can happen, we must keep the deleted page around as
893+
* a tombstone.
894+
*
895+
* Compare the deletion XID with RecentGlobalXmin. If deleteXid <
896+
* RecentGlobalXmin, then no scan that's still in progress could have
897+
* seen its downlink, and we can recycle it.
898+
*/
899+
FullTransactionIddeletexid_full=GistPageGetDeleteXid(page);
900+
FullTransactionIdrecentxmin_full=GetFullRecentGlobalXmin();
901+
902+
if (FullTransactionIdPrecedes(deletexid_full,recentxmin_full))
903+
return true;
904+
}
905+
return false;
888906
}
889907

890908
bytea*

‎src/backend/access/gist/gistvacuum.c

Lines changed: 3 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -595,7 +595,7 @@ gistdeletepage(IndexVacuumInfo *info, GistBulkDeleteResult *stats,
595595
ItemIdiid;
596596
IndexTupleidxtuple;
597597
XLogRecPtrrecptr;
598-
TransactionIdtxid;
598+
FullTransactionIdtxid;
599599

600600
/*
601601
* Check that the leaf is still empty and deletable.
@@ -648,14 +648,13 @@ gistdeletepage(IndexVacuumInfo *info, GistBulkDeleteResult *stats,
648648
* currently in progress must have ended. (That's much more conservative
649649
* than needed, but let's keep it safe and simple.)
650650
*/
651-
txid=ReadNewTransactionId();
651+
txid=ReadNextFullTransactionId();
652652

653653
START_CRIT_SECTION();
654654

655655
/* mark the page as deleted */
656656
MarkBufferDirty(leafBuffer);
657-
GistPageSetDeleteXid(leafPage,txid);
658-
GistPageSetDeleted(leafPage);
657+
GistPageSetDeleted(leafPage,txid);
659658
stats->stats.pages_deleted++;
660659

661660
/* remove the downlink from the parent */

‎src/backend/access/gist/gistxlog.c

Lines changed: 25 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -356,8 +356,7 @@ gistRedoPageDelete(XLogReaderState *record)
356356
{
357357
Pagepage= (Page)BufferGetPage(leafBuffer);
358358

359-
GistPageSetDeleteXid(page,xldata->deleteXid);
360-
GistPageSetDeleted(page);
359+
GistPageSetDeleted(page,xldata->deleteXid);
361360

362361
PageSetLSN(page,lsn);
363362
MarkBufferDirty(leafBuffer);
@@ -396,8 +395,27 @@ gistRedoPageReuse(XLogReaderState *record)
396395
*/
397396
if (InHotStandby)
398397
{
399-
ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid,
400-
xlrec->node);
398+
FullTransactionIdlatestRemovedFullXid=xlrec->latestRemovedFullXid;
399+
FullTransactionIdnextFullXid=ReadNextFullTransactionId();
400+
uint64diff;
401+
402+
/*
403+
* ResolveRecoveryConflictWithSnapshot operates on 32-bit
404+
* TransactionIds, so truncate the logged FullTransactionId. If the
405+
* logged value is very old, so that XID wrap-around already happened
406+
* on it, there can't be any snapshots that still see it.
407+
*/
408+
nextFullXid=ReadNextFullTransactionId();
409+
diff=U64FromFullTransactionId(nextFullXid)-
410+
U64FromFullTransactionId(latestRemovedFullXid);
411+
if (diff<MaxTransactionId /2)
412+
{
413+
TransactionIdlatestRemovedXid;
414+
415+
latestRemovedXid=XidFromFullTransactionId(latestRemovedFullXid);
416+
ResolveRecoveryConflictWithSnapshot(latestRemovedXid,
417+
xlrec->node);
418+
}
401419
}
402420
}
403421

@@ -554,7 +572,7 @@ gistXLogSplit(bool page_is_leaf,
554572
* downlink from the parent page.
555573
*/
556574
XLogRecPtr
557-
gistXLogPageDelete(Bufferbuffer,TransactionIdxid,
575+
gistXLogPageDelete(Bufferbuffer,FullTransactionIdxid,
558576
BufferparentBuffer,OffsetNumberdownlinkOffset)
559577
{
560578
gistxlogPageDeletexlrec;
@@ -578,7 +596,7 @@ gistXLogPageDelete(Buffer buffer, TransactionId xid,
578596
* Write XLOG record about reuse of a deleted page.
579597
*/
580598
void
581-
gistXLogPageReuse(Relationrel,BlockNumberblkno,TransactionIdlatestRemovedXid)
599+
gistXLogPageReuse(Relationrel,BlockNumberblkno,FullTransactionIdlatestRemovedXid)
582600
{
583601
gistxlogPageReusexlrec_reuse;
584602

@@ -591,7 +609,7 @@ gistXLogPageReuse(Relation rel, BlockNumber blkno, TransactionId latestRemovedXi
591609
/* XLOG stuff */
592610
xlrec_reuse.node=rel->rd_node;
593611
xlrec_reuse.block=blkno;
594-
xlrec_reuse.latestRemovedXid=latestRemovedXid;
612+
xlrec_reuse.latestRemovedFullXid=latestRemovedXid;
595613

596614
XLogBeginInsert();
597615
XLogRegisterData((char*)&xlrec_reuse,SizeOfGistxlogPageReuse);

‎src/backend/access/rmgrdesc/gistdesc.c

Lines changed: 7 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -26,10 +26,11 @@ out_gistxlogPageUpdate(StringInfo buf, gistxlogPageUpdate *xlrec)
2626
staticvoid
2727
out_gistxlogPageReuse(StringInfobuf,gistxlogPageReuse*xlrec)
2828
{
29-
appendStringInfo(buf,"rel %u/%u/%u; blk %u; latestRemovedXid %u",
29+
appendStringInfo(buf,"rel %u/%u/%u; blk %u; latestRemovedXid %u:%u",
3030
xlrec->node.spcNode,xlrec->node.dbNode,
3131
xlrec->node.relNode,xlrec->block,
32-
xlrec->latestRemovedXid);
32+
EpochFromFullTransactionId(xlrec->latestRemovedFullXid),
33+
XidFromFullTransactionId(xlrec->latestRemovedFullXid));
3334
}
3435

3536
staticvoid
@@ -50,8 +51,10 @@ out_gistxlogPageSplit(StringInfo buf, gistxlogPageSplit *xlrec)
5051
staticvoid
5152
out_gistxlogPageDelete(StringInfobuf,gistxlogPageDelete*xlrec)
5253
{
53-
appendStringInfo(buf,"deleteXid %u; downlink %u",
54-
xlrec->deleteXid,xlrec->downlinkOffset);
54+
appendStringInfo(buf,"deleteXid %u:%u; downlink %u",
55+
EpochFromFullTransactionId(xlrec->deleteXid),
56+
XidFromFullTransactionId(xlrec->deleteXid),
57+
xlrec->downlinkOffset);
5558
}
5659

5760
void

‎src/backend/utils/time/snapmgr.c

Lines changed: 30 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -956,6 +956,36 @@ xmin_cmp(const pairingheap_node *a, const pairingheap_node *b, void *arg)
956956
return0;
957957
}
958958

959+
/*
960+
* Get current RecentGlobalXmin value, as a FullTransactionId.
961+
*/
962+
FullTransactionId
963+
GetFullRecentGlobalXmin(void)
964+
{
965+
FullTransactionIdnextxid_full;
966+
uint32nextxid_epoch;
967+
TransactionIdnextxid_xid;
968+
uint32epoch;
969+
970+
Assert(TransactionIdIsNormal(RecentGlobalXmin));
971+
972+
/*
973+
* Compute the epoch from the next XID's epoch. This relies on the fact
974+
* that RecentGlobalXmin must be within the 2 billion XID horizon from the
975+
* next XID.
976+
*/
977+
nextxid_full=ReadNextFullTransactionId();
978+
nextxid_epoch=EpochFromFullTransactionId(nextxid_full);
979+
nextxid_xid=XidFromFullTransactionId(nextxid_full);
980+
981+
if (RecentGlobalXmin>nextxid_xid)
982+
epoch=nextxid_epoch-1;
983+
else
984+
epoch=nextxid_epoch;
985+
986+
returnFullTransactionIdFromEpochAndXid(epoch,RecentGlobalXmin);
987+
}
988+
959989
/*
960990
* SnapshotResetXmin
961991
*

‎src/include/access/gist.h

Lines changed: 40 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -16,6 +16,7 @@
1616
#ifndefGIST_H
1717
#defineGIST_H
1818

19+
#include"access/transam.h"
1920
#include"access/xlog.h"
2021
#include"access/xlogdefs.h"
2122
#include"storage/block.h"
@@ -140,8 +141,6 @@ typedef struct GISTENTRY
140141
#defineGIST_LEAF(entry) (GistPageIsLeaf((entry)->page))
141142

142143
#defineGistPageIsDeleted(page) ( GistPageGetOpaque(page)->flags & F_DELETED)
143-
#defineGistPageSetDeleted(page)( GistPageGetOpaque(page)->flags |= F_DELETED)
144-
#defineGistPageSetNonDeleted(page) ( GistPageGetOpaque(page)->flags &= ~F_DELETED)
145144

146145
#defineGistTuplesDeleted(page) ( GistPageGetOpaque(page)->flags & F_TUPLES_DELETED)
147146
#defineGistMarkTuplesDeleted(page) ( GistPageGetOpaque(page)->flags |= F_TUPLES_DELETED)
@@ -158,9 +157,45 @@ typedef struct GISTENTRY
158157
#defineGistPageGetNSN(page) ( PageXLogRecPtrGet(GistPageGetOpaque(page)->nsn))
159158
#defineGistPageSetNSN(page,val) ( PageXLogRecPtrSet(GistPageGetOpaque(page)->nsn, val))
160159

161-
/* For deleted pages we store last xid which could see the page in scan */
162-
#defineGistPageGetDeleteXid(page) ( ((PageHeader) (page))->pd_prune_xid )
163-
#defineGistPageSetDeleteXid(page,val) ( ((PageHeader) (page))->pd_prune_xid = val)
160+
161+
/*
162+
* On a deleted page, we store this struct. A deleted page doesn't contain any
163+
* tuples, so we don't use the normal page layout with line pointers. Instead,
164+
* this struct is stored right after the standard page header. pd_lower points
165+
* to the end of this struct. If we add fields to this struct in the future, we
166+
* can distinguish the old and new formats by pd_lower.
167+
*/
168+
typedefstructGISTDeletedPageContents
169+
{
170+
/* last xid which could see the page in a scan */
171+
FullTransactionIddeleteXid;
172+
}GISTDeletedPageContents;
173+
174+
staticinlinevoid
175+
GistPageSetDeleted(Pagepage,FullTransactionIddeletexid)
176+
{
177+
Assert(PageIsEmpty(page));
178+
179+
GistPageGetOpaque(page)->flags |=F_DELETED;
180+
((PageHeader)page)->pd_lower=MAXALIGN(SizeOfPageHeaderData)+sizeof(GISTDeletedPageContents);
181+
182+
((GISTDeletedPageContents*)PageGetContents(page))->deleteXid=deletexid;
183+
}
184+
185+
staticinlineFullTransactionId
186+
GistPageGetDeleteXid(Pagepage)
187+
{
188+
Assert(GistPageIsDeleted(page));
189+
190+
/* Is the deleteXid field present? */
191+
if (((PageHeader)page)->pd_lower >=MAXALIGN(SizeOfPageHeaderData)+
192+
offsetof(GISTDeletedPageContents,deleteXid)+sizeof(FullTransactionId))
193+
{
194+
return ((GISTDeletedPageContents*)PageGetContents(page))->deleteXid;
195+
}
196+
else
197+
returnFullTransactionIdFromEpochAndXid(0,FirstNormalTransactionId);
198+
}
164199

165200
/*
166201
* Vector of GISTENTRY structs; user-defined methods union and picksplit

‎src/include/access/gist_private.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -426,11 +426,11 @@ extern SplitedPageLayout *gistSplit(Relation r, Page page, IndexTuple *itup,
426426

427427
/* gistxlog.c */
428428
externXLogRecPtrgistXLogPageDelete(Bufferbuffer,
429-
TransactionIdxid,BufferparentBuffer,
429+
FullTransactionIdxid,BufferparentBuffer,
430430
OffsetNumberdownlinkOffset);
431431

432432
externvoidgistXLogPageReuse(Relationrel,BlockNumberblkno,
433-
TransactionIdlatestRemovedXid);
433+
FullTransactionIdlatestRemovedXid);
434434

435435
externXLogRecPtrgistXLogUpdate(Bufferbuffer,
436436
OffsetNumber*todelete,intntodelete,

‎src/include/access/gistxlog.h

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -83,7 +83,7 @@ typedef struct gistxlogPageSplit
8383
*/
8484
typedefstructgistxlogPageDelete
8585
{
86-
TransactionIddeleteXid;/* last Xid which could see page in scan */
86+
FullTransactionIddeleteXid;/* last Xid which could see page in scan */
8787
OffsetNumberdownlinkOffset;/* Offset of downlink referencing this
8888
* page */
8989
}gistxlogPageDelete;
@@ -98,10 +98,10 @@ typedef struct gistxlogPageReuse
9898
{
9999
RelFileNodenode;
100100
BlockNumberblock;
101-
TransactionIdlatestRemovedXid;
101+
FullTransactionIdlatestRemovedFullXid;
102102
}gistxlogPageReuse;
103103

104-
#defineSizeOfGistxlogPageReuse(offsetof(gistxlogPageReuse,latestRemovedXid) + sizeof(TransactionId))
104+
#defineSizeOfGistxlogPageReuse(offsetof(gistxlogPageReuse,latestRemovedFullXid) + sizeof(FullTransactionId))
105105

106106
externvoidgist_redo(XLogReaderState*record);
107107
externvoidgist_desc(StringInfobuf,XLogReaderState*record);

‎src/include/utils/snapmgr.h

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -13,6 +13,7 @@
1313
#ifndefSNAPMGR_H
1414
#defineSNAPMGR_H
1515

16+
#include"access/transam.h"
1617
#include"fmgr.h"
1718
#include"utils/relcache.h"
1819
#include"utils/resowner.h"
@@ -122,6 +123,8 @@ extern void UnregisterSnapshot(Snapshot snapshot);
122123
externSnapshotRegisterSnapshotOnOwner(Snapshotsnapshot,ResourceOwnerowner);
123124
externvoidUnregisterSnapshotFromOwner(Snapshotsnapshot,ResourceOwnerowner);
124125

126+
externFullTransactionIdGetFullRecentGlobalXmin(void);
127+
125128
externvoidAtSubCommit_Snapshot(intlevel);
126129
externvoidAtSubAbort_Snapshot(intlevel);
127130
externvoidAtEOXact_Snapshot(boolisCommit,boolresetXmin);

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