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Review logical replication tablesync code

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Most importantly, remove optimization in LogicalRepSyncTableStart that
skips the normal walrcv_startstreaming/endstreaming dance.  The
optimization is not critically important for production uses anyway,
since it only fires in cases with no activity, and saves an
uninteresting amount of work even then.  Critically, it obscures bugs by
hiding the interesting code path from test cases.

Also: in GetSubscriptionRelState, remove pointless relation open; access
pg_subscription_rel->srsubstate with GETSTRUCT as is typical rather than
SysCacheGetAttr; remove unused 'missing_ok' argument.
In wait_for_relation_state_change, use explicit catalog snapshot
invalidation rather than obscurely (and expensively) through
GetLatestSnapshot.
In various places: sprinkle comments more liberally and rewrite a number
of them.  Other cosmetic code improvements.

No backpatch, since no bug is being fixed here.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Petr Jelínek <petr.jelinek@2ndquadrant.com>
Discussion: https://postgr.es/m/20201010190637.GA5774@alvherre.pgsql
This commit is contained in:
Alvaro Herrera
2020-10-15 11:33:48 -03:00
parent c5b097f8fa
commit b05fe7b442
5 changed files with 131 additions and 178 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
src/backend/replication/logical/worker.c
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@ -2060,6 +2060,7 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
{
TimestampTz last_recv_timestamp = GetCurrentTimestamp();
bool ping_sent = false;
TimeLineID tli;
/*
* Init the ApplyMessageContext which we clean up after each replication
@ -2201,12 +2202,7 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
/* Check if we need to exit the streaming loop. */
if (endofstream)
{
TimeLineID tli;
walrcv_endstreaming(wrconn, &tli);
break;
}
/*
* Wait for more data or latch. If we have unflushed transactions,
@ -2283,6 +2279,9 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
send_feedback(last_received, requestReply, requestReply);
}
}
/* All done */
walrcv_endstreaming(wrconn, &tli);
}
/*
@ -3024,10 +3023,8 @@ ApplyWorkerMain(Datum main_arg)
/* This is table synchronization worker, call initial sync. */
syncslotname = LogicalRepSyncTableStart(&origin_startpos);
/* The slot name needs to be allocated in permanent memory context. */
oldctx = MemoryContextSwitchTo(ApplyContext);
myslotname = pstrdup(syncslotname);
MemoryContextSwitchTo(oldctx);
/* allocate slot name in long-lived context */
myslotname = MemoryContextStrdup(ApplyContext, syncslotname);
pfree(syncslotname);
}