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Commita455878

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Rename PGPROC fields related to group XID clearing again.
Commit0e141c0 introduced a newfacility to reduce ProcArrayLock contention by clearing several XIDsfrom the ProcArray under a single lock acquisition. The namesinitially chosen were deemed not to be very good choices, so commit4aec498 renamed them. But now itseems like we still didn't get it right. A pending patch wants toadd similar infrastructure for batching CLOG updates, so the namesneed to be clear enough to allow a new set of structure members witha related purpose.Amit Kapila
1 parent4c9864b commita455878

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3 files changed

+28
-22
lines changed

3 files changed

+28
-22
lines changed

‎src/backend/storage/ipc/procarray.c‎

Lines changed: 14 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -497,14 +497,14 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
497497
Assert(TransactionIdIsValid(allPgXact[proc->pgprocno].xid));
498498

499499
/* Add ourselves to the list of processes needing a group XID clear. */
500-
proc->clearXid= true;
501-
proc->backendLatestXid=latestXid;
500+
proc->procArrayGroupMember= true;
501+
proc->procArrayGroupMemberXid=latestXid;
502502
while (true)
503503
{
504-
nextidx=pg_atomic_read_u32(&procglobal->firstClearXidElem);
505-
pg_atomic_write_u32(&proc->nextClearXidElem,nextidx);
504+
nextidx=pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
505+
pg_atomic_write_u32(&proc->procArrayGroupNext,nextidx);
506506

507-
if (pg_atomic_compare_exchange_u32(&procglobal->firstClearXidElem,
507+
if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
508508
&nextidx,
509509
(uint32)proc->pgprocno))
510510
break;
@@ -523,12 +523,12 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
523523
{
524524
/* acts as a read barrier */
525525
PGSemaphoreLock(&proc->sem);
526-
if (!proc->clearXid)
526+
if (!proc->procArrayGroupMember)
527527
break;
528528
extraWaits++;
529529
}
530530

531-
Assert(pg_atomic_read_u32(&proc->nextClearXidElem)==INVALID_PGPROCNO);
531+
Assert(pg_atomic_read_u32(&proc->procArrayGroupNext)==INVALID_PGPROCNO);
532532

533533
/* Fix semaphore count for any absorbed wakeups */
534534
while (extraWaits-->0)
@@ -546,8 +546,8 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
546546
*/
547547
while (true)
548548
{
549-
nextidx=pg_atomic_read_u32(&procglobal->firstClearXidElem);
550-
if (pg_atomic_compare_exchange_u32(&procglobal->firstClearXidElem,
549+
nextidx=pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
550+
if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
551551
&nextidx,
552552
INVALID_PGPROCNO))
553553
break;
@@ -562,10 +562,10 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
562562
PGPROC*proc=&allProcs[nextidx];
563563
PGXACT*pgxact=&allPgXact[nextidx];
564564

565-
ProcArrayEndTransactionInternal(proc,pgxact,proc->backendLatestXid);
565+
ProcArrayEndTransactionInternal(proc,pgxact,proc->procArrayGroupMemberXid);
566566

567567
/* Move to next proc in list. */
568-
nextidx=pg_atomic_read_u32(&proc->nextClearXidElem);
568+
nextidx=pg_atomic_read_u32(&proc->procArrayGroupNext);
569569
}
570570

571571
/* We're done with the lock now. */
@@ -582,13 +582,13 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
582582
{
583583
PGPROC*proc=&allProcs[wakeidx];
584584

585-
wakeidx=pg_atomic_read_u32(&proc->nextClearXidElem);
586-
pg_atomic_write_u32(&proc->nextClearXidElem,INVALID_PGPROCNO);
585+
wakeidx=pg_atomic_read_u32(&proc->procArrayGroupNext);
586+
pg_atomic_write_u32(&proc->procArrayGroupNext,INVALID_PGPROCNO);
587587

588588
/* ensure all previous writes are visible before follower continues. */
589589
pg_write_barrier();
590590

591-
proc->clearXid= false;
591+
proc->procArrayGroupMember= false;
592592

593593
if (proc!=MyProc)
594594
PGSemaphoreUnlock(&proc->sem);

‎src/backend/storage/lmgr/proc.c‎

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -181,7 +181,7 @@ InitProcGlobal(void)
181181
ProcGlobal->startupBufferPinWaitBufId=-1;
182182
ProcGlobal->walwriterLatch=NULL;
183183
ProcGlobal->checkpointerLatch=NULL;
184-
pg_atomic_init_u32(&ProcGlobal->firstClearXidElem,INVALID_PGPROCNO);
184+
pg_atomic_init_u32(&ProcGlobal->procArrayGroupFirst,INVALID_PGPROCNO);
185185

186186
/*
187187
* Create and initialize all the PGPROC structures we'll need. There are
@@ -396,9 +396,9 @@ InitProcess(void)
396396
SHMQueueElemInit(&(MyProc->syncRepLinks));
397397

398398
/* Initialize fields for group XID clearing. */
399-
MyProc->clearXid= false;
400-
MyProc->backendLatestXid=InvalidTransactionId;
401-
pg_atomic_init_u32(&MyProc->nextClearXidElem,INVALID_PGPROCNO);
399+
MyProc->procArrayGroupMember= false;
400+
MyProc->procArrayGroupMemberXid=InvalidTransactionId;
401+
pg_atomic_init_u32(&MyProc->procArrayGroupNext,INVALID_PGPROCNO);
402402

403403
/* Check that group locking fields are in a proper initial state. */
404404
Assert(MyProc->lockGroupLeaderIdentifier==0);

‎src/include/storage/proc.h‎

Lines changed: 10 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -142,9 +142,15 @@ struct PGPROC
142142
structXidCachesubxids;/* cache for subtransaction XIDs */
143143

144144
/* Support for group XID clearing. */
145-
boolclearXid;
146-
pg_atomic_uint32nextClearXidElem;
147-
TransactionIdbackendLatestXid;
145+
/* true, if member of ProcArray group waiting for XID clear */
146+
boolprocArrayGroupMember;
147+
/* next ProcArray group member waiting for XID clear */
148+
pg_atomic_uint32procArrayGroupNext;
149+
/*
150+
* latest transaction id among the transaction's main XID and
151+
* subtransactions
152+
*/
153+
TransactionIdprocArrayGroupMemberXid;
148154

149155
/* Per-backend LWLock. Protects fields below. */
150156
LWLockbackendLock;
@@ -217,7 +223,7 @@ typedef struct PROC_HDR
217223
/* Head of list of bgworker free PGPROC structures */
218224
PGPROC*bgworkerFreeProcs;
219225
/* First pgproc waiting for group XID clear */
220-
pg_atomic_uint32firstClearXidElem;
226+
pg_atomic_uint32procArrayGroupFirst;
221227
/* WALWriter process's latch */
222228
Latch*walwriterLatch;
223229
/* Checkpointer process's latch */

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