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Commit9a56dc3

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Fix various possible problems with synchronous replication.
1. Don't ignore query cancel interrupts. Instead, if the user asks tocancel the query after we've already committed it, but before it's onthe standby, just emit a warning and let the COMMIT finish.2. Don't ignore die interrupts (pg_terminate_backend or fast shutdown).Instead, emit a warning message and close the connection withoutacknowledging the commit. Other backends will still see the effect ofthe commit, but there's no getting around that; it's too late to abortat this point, and ignoring die interrupts altogether doesn't seem likea good idea.3. If synchronous_standby_names becomes empty, wake up all backendswaiting for synchronous replication to complete. Without this, someoneattempting to shut synchronous replication off could easily wedge theentire system instead.4. Avoid depending on the assumption that if a walsender updatesMyProc->syncRepState, we'll see the change even if we read it withoutholding the lock. The window for this appears to be quite narrow (andprobably doesn't exist at all on machines with strong memory ordering)but protecting against it is practically free, so do that.5. Remove useless state SYNC_REP_MUST_DISCONNECT, which isn't needed anddoesn't actually do anything.There's still some further work needed here to make the behavior of fastshutdown plausible, but that looks complex, so I'm leaving it for aseparate commit. Review by Fujii Masao.
1 parente148443 commit9a56dc3

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6 files changed

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‎doc/src/sgml/config.sgml

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@@ -2100,8 +2100,7 @@ SET ENABLE_SEQSCAN TO OFF;
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If a standby is removed from the list of servers then it will stop
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being the synchronous standby, allowing another to take its place.
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If the list is empty, synchronous replication will not be
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possible, whatever the setting of <varname>synchronous_replication</>,
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however, already waiting commits will continue to wait.
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possible, whatever the setting of <varname>synchronous_replication</>.
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Standbys may also be added to the list without restarting the server.
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</para>
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</listitem>

‎src/backend/postmaster/walwriter.c

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Original file line numberDiff line numberDiff line change
@@ -49,6 +49,7 @@
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#include"libpq/pqsignal.h"
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#include"miscadmin.h"
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#include"postmaster/walwriter.h"
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#include"replication/syncrep.h"
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#include"storage/bufmgr.h"
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#include"storage/fd.h"
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#include"storage/ipc.h"
@@ -216,6 +217,9 @@ WalWriterMain(void)
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*/
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PG_SETMASK(&UnBlockSig);
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/* Do this once before starting the loop, then just at SIGHUP time. */
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SyncRepUpdateSyncStandbysDefined();
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/*
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* Loop forever
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*/
@@ -237,6 +241,8 @@ WalWriterMain(void)
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{
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got_SIGHUP= false;
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ProcessConfigFile(PGC_SIGHUP);
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/* update global shmem state for sync rep */
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SyncRepUpdateSyncStandbysDefined();
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}
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if (shutdown_requested)
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{

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