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Commit4cd3fb6

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Truncate predicate lock manager's SLRU lazily at checkpoint. That's safer
than doing it aggressively whenever the tail-XID pointer is advanced, becausethis way we don't need to do it while holding SerializableXactHashLock.This also fixes bug #5915 spotted by YAMAMOTO Takashi, and removes anobsolete comment spotted by Kevin Grittner.
1 parent804d13a commit4cd3fb6

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3 files changed

+69
-52
lines changed

3 files changed

+69
-52
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -48,6 +48,7 @@
4848
#include"storage/ipc.h"
4949
#include"storage/latch.h"
5050
#include"storage/pmsignal.h"
51+
#include"storage/predicate.h"
5152
#include"storage/procarray.h"
5253
#include"storage/reinit.h"
5354
#include"storage/smgr.h"
@@ -7875,6 +7876,7 @@ CheckPointGuts(XLogRecPtr checkPointRedo, int flags)
78757876
CheckPointCLOG();
78767877
CheckPointSUBTRANS();
78777878
CheckPointMultiXact();
7879+
CheckPointPredicate();
78787880
CheckPointRelationMap();
78797881
CheckPointBuffers(flags);/* performs all required fsyncs */
78807882
/* We deliberately delay 2PC checkpointing as long as possible */

‎src/backend/storage/lmgr/predicate.c

Lines changed: 65 additions & 52 deletions
Original file line numberDiff line numberDiff line change
@@ -323,10 +323,9 @@ static SlruCtlData OldSerXidSlruCtlData;
323323

324324
typedefstructOldSerXidControlData
325325
{
326-
intheadPage;
327-
inttailSegment;
328-
TransactionIdheadXid;
329-
TransactionIdtailXid;
326+
intheadPage;/* newest initialized page */
327+
TransactionIdheadXid;/* newest valid Xid in the SLRU */
328+
TransactionIdtailXid;/* oldest xmin we might be interested in */
330329
boolwarningIssued;
331330
}OldSerXidControlData;
332331

@@ -711,7 +710,6 @@ OldSerXidInit(void)
711710
* Set control information to reflect empty SLRU.
712711
*/
713712
oldSerXidControl->headPage=-1;
714-
oldSerXidControl->tailSegment=-1;
715713
oldSerXidControl->headXid=InvalidTransactionId;
716714
oldSerXidControl->tailXid=InvalidTransactionId;
717715
oldSerXidControl->warningIssued= false;
@@ -722,18 +720,14 @@ OldSerXidInit(void)
722720
* Record a committed read write serializable xid and the minimum
723721
* commitSeqNo of any transactions to which this xid had a rw-conflict out.
724722
* A zero seqNo means that there were no conflicts out from xid.
725-
*
726-
* The return value is normally false -- true means that we're about to
727-
* wrap around our space for tracking these xids, so the caller might want
728-
* to take action to prevent that.
729723
*/
730724
staticvoid
731725
OldSerXidAdd(TransactionIdxid,SerCommitSeqNominConflictCommitSeqNo)
732726
{
733727
TransactionIdtailXid;
734728
inttargetPage;
735729
intslotno;
736-
intpage;
730+
intfirstZeroPage;
737731
intxidSpread;
738732
boolisNewPage;
739733

@@ -745,30 +739,34 @@ OldSerXidAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo)
745739

746740
/*
747741
* If no serializable transactions are active, there shouldn't be anything
748-
* to push out tothis SLRU. Hitting this assert would mean there's
742+
* to push out tothe SLRU. Hitting this assert would mean there's
749743
* something wrong with the earlier cleanup logic.
750744
*/
751745
tailXid=oldSerXidControl->tailXid;
752746
Assert(TransactionIdIsValid(tailXid));
753747

748+
/*
749+
* If the SLRU is currently unused, zero out the whole active region
750+
* from tailXid to headXid before taking it into use. Otherwise zero
751+
* out only any new pages that enter the tailXid-headXid range as we
752+
* advance headXid.
753+
*/
754754
if (oldSerXidControl->headPage<0)
755755
{
756-
page=OldSerXidPage(tailXid);
757-
oldSerXidControl->tailSegment=OldSerXidSegment(page);
758-
page=oldSerXidControl->tailSegment*OLDSERXID_ENTRIESPERPAGE;
756+
firstZeroPage=OldSerXidPage(tailXid);
759757
isNewPage= true;
760758
}
761759
else
762760
{
763-
page=OldSerXidNextPage(oldSerXidControl->headPage);
764-
isNewPage=OldSerXidPagePrecedesLogically(oldSerXidControl->headPage,targetPage);
761+
firstZeroPage=OldSerXidNextPage(oldSerXidControl->headPage);
762+
isNewPage=OldSerXidPagePrecedesLogically(oldSerXidControl->headPage,
763+
targetPage);
765764
}
766765

767766
if (!TransactionIdIsValid(oldSerXidControl->headXid)
768767
||TransactionIdFollows(xid,oldSerXidControl->headXid))
769768
oldSerXidControl->headXid=xid;
770-
if (oldSerXidControl->headPage<0
771-
||OldSerXidPagePrecedesLogically(oldSerXidControl->headPage,targetPage))
769+
if (isNewPage)
772770
oldSerXidControl->headPage=targetPage;
773771

774772
xidSpread= (((uint32)xid)- ((uint32)tailXid));
@@ -788,10 +786,10 @@ OldSerXidAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo)
788786
if (isNewPage)
789787
{
790788
/* Initialize intervening pages. */
791-
while (page!=targetPage)
789+
while (firstZeroPage!=targetPage)
792790
{
793-
(void)SimpleLruZeroPage(OldSerXidSlruCtl,page);
794-
page=OldSerXidNextPage(page);
791+
(void)SimpleLruZeroPage(OldSerXidSlruCtl,firstZeroPage);
792+
firstZeroPage=OldSerXidNextPage(firstZeroPage);
795793
}
796794
slotno=SimpleLruZeroPage(OldSerXidSlruCtl,targetPage);
797795
}
@@ -846,31 +844,24 @@ OldSerXidGetMinConflictCommitSeqNo(TransactionId xid)
846844
/*
847845
* Call this whenever there is a new xmin for active serializable
848846
* transactions. We don't need to keep information on transactions which
849-
*preceed that. InvalidTransactionId means none active, so everything in
850-
* the SLRUshould be discarded.
847+
*precede that. InvalidTransactionId means none active, so everything in
848+
* the SLRUcan be discarded.
851849
*/
852850
staticvoid
853851
OldSerXidSetActiveSerXmin(TransactionIdxid)
854852
{
855-
intnewTailPage;
856-
intnewTailSegment;
857-
858853
LWLockAcquire(OldSerXidLock,LW_EXCLUSIVE);
859854

860855
/*
861856
* When no sxacts are active, nothing overlaps, set the xid values to
862-
* invalid to show that there are no valid entries. Don't clear the
863-
* segment/page information, though. A new xmin might still land in an
864-
* existing segment, and we don't want to repeatedly delete and re-create
865-
* the same segment file.
857+
* invalid to show that there are no valid entries. Don't clear headPage,
858+
* though. A new xmin might still land on that page, and we don't want
859+
* to repeatedly zero out the same page.
866860
*/
867861
if (!TransactionIdIsValid(xid))
868862
{
869-
if (TransactionIdIsValid(oldSerXidControl->tailXid))
870-
{
871-
oldSerXidControl->headXid=InvalidTransactionId;
872-
oldSerXidControl->tailXid=InvalidTransactionId;
873-
}
863+
oldSerXidControl->tailXid=InvalidTransactionId;
864+
oldSerXidControl->headXid=InvalidTransactionId;
874865
LWLockRelease(OldSerXidLock);
875866
return;
876867
}
@@ -886,7 +877,9 @@ OldSerXidSetActiveSerXmin(TransactionId xid)
886877
Assert(oldSerXidControl->headPage<0);
887878
if (!TransactionIdIsValid(oldSerXidControl->tailXid)
888879
||TransactionIdPrecedes(xid,oldSerXidControl->tailXid))
880+
{
889881
oldSerXidControl->tailXid=xid;
882+
}
890883
LWLockRelease(OldSerXidLock);
891884
return;
892885
}
@@ -896,37 +889,57 @@ OldSerXidSetActiveSerXmin(TransactionId xid)
896889

897890
oldSerXidControl->tailXid=xid;
898891

899-
/* Exit quickly if there are no segments active. */
892+
LWLockRelease(OldSerXidLock);
893+
}
894+
895+
/*
896+
* Perform a checkpoint --- either during shutdown, or on-the-fly
897+
*
898+
* We don't have any data that needs to survive a restart, but this is a
899+
* convenient place to truncate the SLRU.
900+
*/
901+
void
902+
CheckPointPredicate(void)
903+
{
904+
inttailPage;
905+
906+
LWLockAcquire(OldSerXidLock,LW_EXCLUSIVE);
907+
908+
/* Exit quickly if the SLRU is currently not in use. */
900909
if (oldSerXidControl->headPage<0)
901910
{
902911
LWLockRelease(OldSerXidLock);
903912
return;
904913
}
905914

906-
newTailPage=OldSerXidPage(xid);
907-
newTailSegment=OldSerXidSegment(newTailPage);
908-
909-
/* Exit quickly if we're still on the same segment. */
910-
if (newTailSegment==oldSerXidControl->tailSegment)
915+
if (TransactionIdIsValid(oldSerXidControl->tailXid))
911916
{
912-
LWLockRelease(OldSerXidLock);
913-
return;
917+
/* We can truncate the SLRU up to the page containing tailXid */
918+
tailPage=OldSerXidPage(oldSerXidControl->tailXid);
914919
}
915-
916-
oldSerXidControl->tailSegment=newTailSegment;
917-
918-
/* See if that has cleared the last segment. */
919-
if (OldSerXidPagePrecedesLogically(oldSerXidControl->headPage,
920-
newTailSegment*SLRU_PAGES_PER_SEGMENT))
920+
else
921921
{
922-
oldSerXidControl->headXid=InvalidTransactionId;
922+
/*
923+
* The SLRU is no longer needed. Truncate everything but the last
924+
* page. We don't dare to touch the last page in case the SLRU is
925+
* taken back to use, and the new tail falls on the same page.
926+
*/
927+
tailPage=oldSerXidControl->headPage;
923928
oldSerXidControl->headPage=-1;
924-
oldSerXidControl->tailSegment=-1;
925929
}
926930

927931
LWLockRelease(OldSerXidLock);
928932

929-
SimpleLruTruncate(OldSerXidSlruCtl,newTailPage);
933+
/*
934+
* Flush dirty SLRU pages to disk
935+
*
936+
* This is not actually necessary from a correctness point of view. We do
937+
* it merely as a debugging aid.
938+
*/
939+
SimpleLruFlush(OldSerXidSlruCtl, true);
940+
941+
/* Truncate away pages that are no longer required */
942+
SimpleLruTruncate(OldSerXidSlruCtl,tailPage);
930943
}
931944

932945
/*------------------------------------------------------------------------*/

‎src/include/storage/predicate.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -36,6 +36,8 @@ extern intmax_predicate_locks_per_xact;
3636
externvoidInitPredicateLocks(void);
3737
externSizePredicateLockShmemSize(void);
3838

39+
externvoidCheckPointPredicate(void);
40+
3941
/* predicate lock reporting */
4042
externboolPageIsPredicateLocked(constRelationrelation,constBlockNumberblkno);
4143

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