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"standby switchover": avoid potential race condition with WAL location check

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Immediately after the demotion candidate (primary) has shut down, we can't
be absolutely sure that the walreceiver has flushed all WAL to disk, so
checking pg_last_wal_receive_lsn() at that point might not reflect
the actual last available WAL location.

To handle this, we'll loop for a while (timeout controlled by configuration
parameter "wal_receive_check_timeout") before finally deciding whether
the standby is still behind the shut-down primary.

Addresses issue raised in GitHub #518.
This commit is contained in:
Ian Barwick
2019-02-01 11:59:30 +09:00
parent f04f2af8aa
commit 9273e7af73
8 changed files with 78 additions and 22 deletions
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3
configfile.c
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@@ -335,6 +335,7 @@ _parse_config(t_configuration_options *options, ItemList *error_list, ItemList *
*/
options->shutdown_check_timeout = DEFAULT_SHUTDOWN_CHECK_TIMEOUT;
options->standby_reconnect_timeout = DEFAULT_STANDBY_RECONNECT_TIMEOUT;
options->wal_receive_check_timeout = DEFAULT_WAL_RECEIVE_CHECK_TIMEOUT;
/*-----------------
* repmgrd settings
@@ -557,6 +558,8 @@ _parse_config(t_configuration_options *options, ItemList *error_list, ItemList *
options->shutdown_check_timeout = repmgr_atoi(value, name, error_list, 0);
else if (strcmp(name, "standby_reconnect_timeout") == 0)
options->standby_reconnect_timeout = repmgr_atoi(value, name, error_list, 0);
else if (strcmp(name, "wal_receive_check_timeout") == 0)
options->wal_receive_check_timeout = repmgr_atoi(value, name, error_list, 0);
/* node rejoin settings */
else if (strcmp(name, "node_rejoin_timeout") == 0)