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Commitc79c570

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Small comment fixes and enhancements.
1 parentbb8f0c4 commitc79c570

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3 files changed

+39
-14
lines changed

3 files changed

+39
-14
lines changed

‎src/backend/storage/lmgr/README-SSI

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -389,7 +389,7 @@ locks.
389389

390390
* Because PostgreSQL does not have the same concept of an "oldest
391391
transaction ID" for all serializable transactions as assumed in the
392-
Cahillthese, we track the oldest snapshot xmin among serializable
392+
Cahillthesis, we track the oldest snapshot xmin among serializable
393393
transactions, and a count of how many active transactions use that
394394
xmin. When the count hits zero we find the new oldest xmin and run a
395395
clean-up based on that.

‎src/backend/storage/lmgr/predicate.c

Lines changed: 36 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -703,8 +703,8 @@ OldSerXidInit(void)
703703
* Set up SLRU management of the pg_serial data.
704704
*/
705705
OldSerXidSlruCtl->PagePrecedes=OldSerXidPagePrecedesLogically;
706-
SimpleLruInit(OldSerXidSlruCtl,"OldSerXid SLRU Ctl",NUM_OLDSERXID_BUFFERS,0,
707-
OldSerXidLock,"pg_serial");
706+
SimpleLruInit(OldSerXidSlruCtl,"OldSerXid SLRU Ctl",
707+
NUM_OLDSERXID_BUFFERS,0,OldSerXidLock,"pg_serial");
708708
/* Override default assumption that writes should be fsync'd */
709709
OldSerXidSlruCtl->do_fsync= false;
710710

@@ -2954,7 +2954,8 @@ PredicateLockPageCombine(const Relation relation, const BlockNumber oldblkno,
29542954
}
29552955

29562956
/*
2957-
* Walk the hash table and find the new xmin.
2957+
* Walk the list of in-progress serializable transactions and find the new
2958+
* xmin.
29582959
*/
29592960
staticvoid
29602961
SetNewSxactGlobalXmin(void)
@@ -3126,6 +3127,10 @@ ReleasePredicateLocks(const bool isCommit)
31263127
&& !SxactIsReadOnly(MySerializableXact)
31273128
&&SxactHasSummaryConflictOut(MySerializableXact))
31283129
{
3130+
/*
3131+
* we don't know which old committed transaction we conflicted with,
3132+
* so be conservative and use FirstNormalSerCommitSeqNo here
3133+
*/
31293134
MySerializableXact->SeqNo.earliestOutConflictCommit=
31303135
FirstNormalSerCommitSeqNo;
31313136
MySerializableXact->flags |=SXACT_FLAG_CONFLICT_OUT;
@@ -3320,14 +3325,19 @@ ReleasePredicateLocksIfROSafe(void)
33203325
}
33213326

33223327
/*
3323-
* Clear old predicate locks.
3328+
* Clear old predicate locks, belonging to committed transactions that are no
3329+
* longer interesting to any in-progress transaction.
33243330
*/
33253331
staticvoid
33263332
ClearOldPredicateLocks(void)
33273333
{
33283334
SERIALIZABLEXACT*finishedSxact;
33293335
PREDICATELOCK*predlock;
33303336

3337+
/*
3338+
* Loop through finished transactions. They are in commit order, so we can
3339+
* stop as soon as we find one that's still interesting.
3340+
*/
33313341
LWLockAcquire(SerializableFinishedListLock,LW_EXCLUSIVE);
33323342
finishedSxact= (SERIALIZABLEXACT*)
33333343
SHMQueueNext(FinishedSerializableTransactions,
@@ -3346,6 +3356,10 @@ ClearOldPredicateLocks(void)
33463356
||TransactionIdPrecedesOrEquals(finishedSxact->finishedBefore,
33473357
PredXact->SxactGlobalXmin))
33483358
{
3359+
/*
3360+
* This transaction committed before any in-progress transaction
3361+
* took its snapshot. It's no longer interesting.
3362+
*/
33493363
LWLockRelease(SerializableXactHashLock);
33503364
SHMQueueDelete(&(finishedSxact->finishedLink));
33513365
ReleaseOneSerializableXact(finishedSxact, false, false);
@@ -3362,7 +3376,10 @@ ClearOldPredicateLocks(void)
33623376
LWLockAcquire(SerializableXactHashLock,LW_SHARED);
33633377
}
33643378
else
3379+
{
3380+
/* Still interesting. */
33653381
break;
3382+
}
33663383
finishedSxact=nextSxact;
33673384
}
33683385
LWLockRelease(SerializableXactHashLock);
@@ -3391,25 +3408,27 @@ ClearOldPredicateLocks(void)
33913408
canDoPartialCleanup= (predlock->commitSeqNo <=PredXact->CanPartialClearThrough);
33923409
LWLockRelease(SerializableXactHashLock);
33933410

3411+
/*
3412+
* If this lock originally belonged to an old enough transaction, we
3413+
* can release it.
3414+
*/
33943415
if (canDoPartialCleanup)
33953416
{
33963417
PREDICATELOCKTAGtag;
3397-
SHM_QUEUE*targetLink;
33983418
PREDICATELOCKTARGET*target;
33993419
PREDICATELOCKTARGETTAGtargettag;
34003420
uint32targettaghash;
34013421
LWLockIdpartitionLock;
34023422

34033423
tag=predlock->tag;
3404-
targetLink=&(predlock->targetLink);
34053424
target=tag.myTarget;
34063425
targettag=target->tag;
34073426
targettaghash=PredicateLockTargetTagHashCode(&targettag);
34083427
partitionLock=PredicateLockHashPartitionLock(targettaghash);
34093428

34103429
LWLockAcquire(partitionLock,LW_EXCLUSIVE);
34113430

3412-
SHMQueueDelete(targetLink);
3431+
SHMQueueDelete(&(predlock->targetLink));
34133432
SHMQueueDelete(&(predlock->xactLink));
34143433

34153434
hash_search_with_hash_value(PredicateLockHash,&tag,
@@ -3437,9 +3456,9 @@ ClearOldPredicateLocks(void)
34373456
* delete the transaction.
34383457
*
34393458
* When the partial flag is set, we can release all predicate locks and
3440-
*out-conflict information -- we've established that there are no longer
3459+
*in-conflict information -- we've established that there are no longer
34413460
* any overlapping read write transactions for which this transaction could
3442-
* matter.
3461+
* matter -- but keep the transaction entry itself and any outConflicts.
34433462
*
34443463
* When the summarize flag is set, we've run short of room for sxact data
34453464
* and must summarize to the SLRU.Predicate locks are transferred to a
@@ -3460,6 +3479,10 @@ ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
34603479
Assert(SxactIsRolledBack(sxact)||SxactIsCommitted(sxact));
34613480
Assert(LWLockHeldByMe(SerializableFinishedListLock));
34623481

3482+
/*
3483+
* First release all the predicate locks held by this xact (or transfer
3484+
* them to OldCommittedSxact if summarize is true)
3485+
*/
34633486
LWLockAcquire(SerializablePredicateLockListLock,LW_SHARED);
34643487
predlock= (PREDICATELOCK*)
34653488
SHMQueueNext(&(sxact->predicateLocks),
@@ -3545,9 +3568,9 @@ ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
35453568
sxidtag.xid=sxact->topXid;
35463569
LWLockAcquire(SerializableXactHashLock,LW_EXCLUSIVE);
35473570

3571+
/* Release all outConflicts (unless 'partial' is true) */
35483572
if (!partial)
35493573
{
3550-
/* Release all outConflicts. */
35513574
conflict= (RWConflict)
35523575
SHMQueueNext(&sxact->outConflicts,
35533576
&sxact->outConflicts,
@@ -3582,9 +3605,9 @@ ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
35823605
conflict=nextConflict;
35833606
}
35843607

3608+
/* Finally, get rid of the xid and the record of the transaction itself. */
35853609
if (!partial)
35863610
{
3587-
/* Get rid of the xid and the record of the transaction itself. */
35883611
if (sxidtag.xid!=InvalidTransactionId)
35893612
hash_search(SerializableXidHash,&sxidtag,HASH_REMOVE,NULL);
35903613
ReleasePredXact(sxact);
@@ -3844,7 +3867,8 @@ CheckForSerializableConflictOut(const bool visible, const Relation relation,
38443867
}
38453868

38463869
/*
3847-
* Check a particular target for rw-dependency conflict in.
3870+
* Check a particular target for rw-dependency conflict in. A subroutine of
3871+
* CheckForSerializableConflictIn().
38483872
*/
38493873
staticvoid
38503874
CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG*targettag)

‎src/include/storage/predicate_internals.h

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -134,7 +134,8 @@ typedef struct PredXactListData
134134
/*
135135
* These global variables are maintained when registering and cleaning up
136136
* serializable transactions. They must be global across all backends,
137-
* but are not needed outside the predicate.c source file.
137+
* but are not needed outside the predicate.c source file. Protected
138+
* by SerializableXactHashLock.
138139
*/
139140
TransactionIdSxactGlobalXmin;/* global xmin for active serializable
140141
* transactions */

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