PostgreSQL 10.0 preview 功能增强 - 增加ProcArrayGroupUpdate等待事件

xiaoxiao2025-09-14 39

背景

ProcArrayGroupUpdate等待事件，指事务结束后，将当前xid从ProcArray移除的事件。

506 /* 507 * If the list was not empty, the leader will clear our XID. It is 508 * impossible to have followers without a leader because the first process 509 * that has added itself to the list will always have nextidx as 510 * INVALID_PGPROCNO. 511 */ 512 if (nextidx != INVALID_PGPROCNO) 513 { 514 int extraWaits = 0; 515 516 /* Sleep until the leader clears our XID. */ 517 pgstat_report_wait_start(WAIT_EVENT_PROCARRAY_GROUP_UPDATE); 518 for (;;) 519 { 520 /* acts as a read barrier */ 521 PGSemaphoreLock(proc->sem); 522 if (!proc->procArrayGroupMember) 523 break; 524 extraWaits++; 525 } 526 pgstat_report_wait_end(); 527 528 Assert(pg_atomic_read_u32(&proc->procArrayGroupNext) == INVALID_PGPROCNO); 529 530 /* Fix semaphore count for any absorbed wakeups */ 531 while (extraWaits-- > 0) 532 PGSemaphoreUnlock(proc->sem); 533 return; 534 }

patch 如下

Add ProcArrayGroupUpdate wait event. author Robert Haas <rhaas@postgresql.org> Sat, 8 Apr 2017 01:41:47 +0800 (13:41 -0400) committer Robert Haas <rhaas@postgresql.org> Sat, 8 Apr 2017 01:41:47 +0800 (13:41 -0400) commit d4116a771925379c33cf4c6634ca620ed08b551d tree 27f53d0c2833c66a78809bdb2db57c23d20cb0b9 tree | snapshot parent dbb2a931478a397a2b655eb77e8be8c1ca136f63 commit | diff Add ProcArrayGroupUpdate wait event. Discussion: http://postgr.es/m/CA+TgmobgWHcXDcChX2+BqJDk2dkPVF85ZrJFhUyHHQmw8diTpA@mail.gmail.com

这个patch的讨论，详见邮件组，本文末尾URL。

PostgreSQL社区的作风非常严谨，一个patch可能在邮件组中讨论几个月甚至几年，根据大家的意见反复的修正，patch合并到master已经非常成熟，所以PostgreSQL的稳定性也是远近闻名的。

参考

https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=d4116a771925379c33cf4c6634ca620ed08b551d

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PostgreSQL 10.0 preview 功能增强 - 增加ProcArrayGroupUpdate等待事件

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