diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/config.sgml | 45 |
1 files changed, 21 insertions, 24 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index b2c5e4d5dd2..575168ed235 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2220,7 +2220,7 @@ include_dir 'conf.d' Specifies whether transaction commit will wait for WAL records to be written to disk before the command returns a <quote>success</> indication to the client. Valid values are <literal>on</>, - <literal>remote_write</>, <literal>remote_apply</>, <literal>local</>, + <literal>remote_apply</>, <literal>remote_write</>, <literal>local</>, and <literal>off</>. The default, and safe, setting is <literal>on</>. When <literal>off</>, there can be a delay between when success is reported to the client and when the transaction is @@ -2237,36 +2237,33 @@ include_dir 'conf.d' discussion see <xref linkend="wal-async-commit">. </para> <para> - If <xref linkend="guc-synchronous-standby-names"> is set, this + If <xref linkend="guc-synchronous-standby-names"> is non-empty, this parameter also controls whether or not transaction commits will wait - for the transaction's WAL records to be replicated to the standby - server. - When set to <literal>on</>, commits will wait until a reply - from the current synchronous standby indicates it has received + for their WAL records to be replicated to the standby server(s). + When set to <literal>on</>, commits will wait until replies + from the current synchronous standby(s) indicate they have received the commit record of the transaction and flushed it to disk. This - ensures the transaction will not be lost unless both primary and - standby suffer corruption of their database storage. - When set to <literal>remote_apply</>, commits will wait until a reply - from the current synchronous standby indicates it has received the + ensures the transaction will not be lost unless both the primary and + all synchronous standbys suffer corruption of their database storage. + When set to <literal>remote_apply</>, commits will wait until replies + from the current synchronous standby(s) indicate they have received the commit record of the transaction and applied it, so that it has become - visible to queries. - When set to <literal>remote_write</>, commits will wait - until a reply from the current synchronous standby indicates it has + visible to queries on the standby(s). + When set to <literal>remote_write</>, commits will wait until replies + from the current synchronous standby(s) indicate they have received the commit record of the transaction and written it out to - the standby's operating system, but the data has not necessarily - reached stable storage on the standby. This setting is sufficient to - ensure data preservation even if the standby instance of + their operating system. This setting is sufficient to + ensure data preservation even if a standby instance of <productname>PostgreSQL</> were to crash, but not if the standby - suffers an operating-system-level crash. + suffers an operating-system-level crash, since the data has not + necessarily reached stable storage on the standby. + Finally, the setting <literal>local</> causes commits to wait for + local flush to disk, but not for replication. This is not usually + desirable when synchronous replication is in use, but is provided for + completeness. </para> <para> - When synchronous - replication is in use, it will normally be sensible either to wait - for both local flush to disk and replication of WAL records, or - to allow the transaction to commit asynchronously. However, the - setting <literal>local</> is available for transactions that - wish to wait for local flush to disk, but not synchronous replication. - If <varname>synchronous_standby_names</> is not set, the settings + If <varname>synchronous_standby_names</> is empty, the settings <literal>on</>, <literal>remote_apply</>, <literal>remote_write</> and <literal>local</> all provide the same synchronization level: transaction commits only wait for local flush to disk. |