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Commit96f6a0c

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Remove files signaling a standby promotion request at postmaster startup
This commit makes postmaster forcibly remove the files signalinga standby promotion request. Otherwise, the existence of those filescan trigger a promotion too early, whether a user wants that or not.This removal of files is usually unnecessary because they can existonly during a few moments during a standby promotion. Howeverthere is a race condition: if pg_ctl promote is executed and createsthe files during a promotion, the files can stay around even afterthe server is brought up to new master. Then, if new standby startsby using the backup taken from that master, the files can existat the server startup and should be removed in order to avoidan unexpected promotion.Back-patch to 9.1 where promote signal file was introduced.Problem reported by Feike Steenbergen.Original patch by Michael Paquier, modified by me.Discussion: 20150528100705.4686.91426@wrigleys.postgresql.org
1 parentc3e0ddd commit96f6a0c

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3 files changed

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‎src/backend/access/transam/xlog.c

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@@ -11587,6 +11587,16 @@ CheckForStandbyTrigger(void)
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return false;
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}
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/*
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* Remove the files signaling a standby promotion request.
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*/
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void
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RemovePromoteSignalFiles(void)
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{
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unlink(PROMOTE_SIGNAL_FILE);
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unlink(FALLBACK_PROMOTE_SIGNAL_FILE);
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}
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/*
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* Check to see if a promote request has arrived. Should be
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* called by postmaster after receiving SIGUSR1.

‎src/backend/postmaster/postmaster.c

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@@ -1175,6 +1175,27 @@ PostmasterMain(int argc, char *argv[])
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*/
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RemovePgTempFiles();
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/*
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* Forcibly remove the files signaling a standby promotion
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* request. Otherwise, the existence of those files triggers
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* a promotion too early, whether a user wants that or not.
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*
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* This removal of files is usually unnecessary because they
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* can exist only during a few moments during a standby
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* promotion. However there is a race condition: if pg_ctl promote
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* is executed and creates the files during a promotion,
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* the files can stay around even after the server is brought up
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* to new master. Then, if new standby starts by using the backup
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* taken from that master, the files can exist at the server
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* startup and should be removed in order to avoid an unexpected
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* promotion.
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*
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* Note that promotion signal files need to be removed before
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* the startup process is invoked. Because, after that, they can
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* be used by postmaster's SIGUSR1 signal handler.
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*/
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RemovePromoteSignalFiles();
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/*
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* If enabled, start up syslogger collection subprocess
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*/

‎src/include/access/xlog.h

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@@ -261,6 +261,7 @@ extern XLogRecPtr GetRedoRecPtr(void);
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externXLogRecPtrGetInsertRecPtr(void);
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externXLogRecPtrGetFlushRecPtr(void);
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externvoidGetNextXidAndEpoch(TransactionId*xid,uint32*epoch);
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externvoidRemovePromoteSignalFiles(void);
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externboolCheckPromoteSignal(void);
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externvoidWakeupRecovery(void);

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