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When the checkpointer writes the shutdown checkpoint, it checks afterwards whether any WAL has been written since it started and throws a PANIC if so. At that point, only walsenders are still active, so one might think this could not happen, but walsenders can also generate WAL, for instance in BASE_BACKUP and logical decoding related commands (e.g. via hint bits). So they can trigger this panic if such a command is run while the shutdown checkpoint is being written. To fix this, divide the walsender shutdown into two phases. First, checkpointer, itself triggered by postmaster, sends a PROCSIG_WALSND_INIT_STOPPING signal to all walsenders. If the backend is idle or runs an SQL query this causes the backend to shutdown, if logical replication is in progress all existing WAL records are processed followed by a shutdown. Otherwise this causes the walsender to switch to the "stopping" state. In this state, the walsender will reject any further replication commands. The checkpointer begins the shutdown checkpoint once all walsenders are confirmed as stopping. When the shutdown checkpoint finishes, the postmaster sends us SIGUSR2. This instructs walsender to send any outstanding WAL, including the shutdown checkpoint record, wait for it to be replicated to the standby, and then exit. Author: Andres Freund, based on an earlier patch by Michael Paquier Reported-By: Fujii Masao, Andres Freund Reviewed-By: Michael Paquier Discussion: https://postgr.es/m/20170602002912.tqlwn4gymzlxpvs2@alap3.anarazel.de Backpatch: 9.4, where logical decoding was introduced
61 lines
1.9 KiB
C
61 lines
1.9 KiB
C
/*-------------------------------------------------------------------------
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*
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* procsignal.h
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* Routines for interprocess signalling
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*
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*
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* Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/procsignal.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PROCSIGNAL_H
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#define PROCSIGNAL_H
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#include "storage/backendid.h"
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/*
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* Reasons for signalling a Postgres child process (a backend or an auxiliary
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* process, like checkpointer). We can cope with concurrent signals for different
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* reasons. However, if the same reason is signaled multiple times in quick
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* succession, the process is likely to observe only one notification of it.
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* This is okay for the present uses.
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*
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* Also, because of race conditions, it's important that all the signals be
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* defined so that no harm is done if a process mistakenly receives one.
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*/
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typedef enum
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{
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PROCSIG_CATCHUP_INTERRUPT, /* sinval catchup interrupt */
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PROCSIG_NOTIFY_INTERRUPT, /* listen/notify interrupt */
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PROCSIG_WALSND_INIT_STOPPING, /* ask walsenders to prepare for shutdown */
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/* Recovery conflict reasons */
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PROCSIG_RECOVERY_CONFLICT_DATABASE,
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PROCSIG_RECOVERY_CONFLICT_TABLESPACE,
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PROCSIG_RECOVERY_CONFLICT_LOCK,
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PROCSIG_RECOVERY_CONFLICT_SNAPSHOT,
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PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
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PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
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NUM_PROCSIGNALS /* Must be last! */
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} ProcSignalReason;
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/*
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* prototypes for functions in procsignal.c
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*/
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extern Size ProcSignalShmemSize(void);
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extern void ProcSignalShmemInit(void);
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extern void ProcSignalInit(int pss_idx);
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extern int SendProcSignal(pid_t pid, ProcSignalReason reason,
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BackendId backendId);
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extern void procsignal_sigusr1_handler(SIGNAL_ARGS);
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extern PGDLLIMPORT bool set_latch_on_sigusr1;
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#endif /* PROCSIGNAL_H */
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