Hi Michael, Thanks for reviewing!
On 8/29/17 9:44 PM, Michael Paquier wrote: > On Tue, Aug 29, 2017 at 10:59 PM, David Steele <da...@pgmasters.net> wrote: >> >> Attached is the 9.6 patch. It required a bit more work in func.sgml >> than I was expecting so have a close look at that. The rest was mostly >> removing irrelevant hunks. > > + switch to the next WAL segment. On a standby, it is not possible to > + automatically switch WAL segments, so you may wish to run > + <function>pg_switch_wal</function> on the primary to perform a manual > + switch. The reason for the switch is to arrange for > [...] > + WAL segments have been archived. If write activity on the primary > is low, it > + may be useful to run <function>pg_switch_wal</> on the primary in order > to > + trigger an immediate segment switch of the last required WAL > It seems to me that both portions are wrong. There is no archiving > wait on standbys for 9.6, and I think its clearly stated here that pg_stop_backup() does not wait for WAL to archive on a standby. Even, it is very important for the backup routine to make sure that all the WAL *is* archived. > pg_stop_backup triggers by itself the > segment switch, so saying that enforcing pg_switch_wal on the primary > is moot. pg_stop_backup() does not perform a WAL switch on the standby which is what this sentence is referring to. I have separated this section out into a new paragraph to (hopefully) make it clearer. > pg_switch_xlog has been renamed to pg_switch_wal in PG10, so > the former name applies. Whoops! New patch is attached. Thanks, -- -David da...@pgmasters.net
diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml index 03c0dbf1cd..fd696c38db 100644 --- a/doc/src/sgml/backup.sgml +++ b/doc/src/sgml/backup.sgml @@ -889,8 +889,11 @@ SELECT pg_start_backup('label', false, false); <programlisting> SELECT * FROM pg_stop_backup(false); </programlisting> - This terminates the backup mode and performs an automatic switch to - the next WAL segment. The reason for the switch is to arrange for + This terminates backup mode. On a primary, it also performs an automatic + switch to the next WAL segment. On a standby, it is not possible to + automatically switch WAL segments, so you may wish to run + <function>pg_switch_xlog</function> on the primary to perform a manual + switch. The reason for the switch is to arrange for the last WAL segment file written during the backup interval to be ready to archive. </para> @@ -908,7 +911,7 @@ SELECT * FROM pg_stop_backup(false); Once the WAL segment files active during the backup are archived, you are done. The file identified by <function>pg_stop_backup</>'s first return value is the last segment that is required to form a complete set of - backup files. If <varname>archive_mode</> is enabled, + backup files. On a primary, if <varname>archive_mode</> is enabled, <function>pg_stop_backup</> does not return until the last segment has been archived. Archiving of these files happens automatically since you have @@ -924,6 +927,13 @@ SELECT * FROM pg_stop_backup(false); <function>pg_stop_backup</> terminates because of this your backup may not be valid. </para> + + <para> + Note that on a standby <function>pg_stop_backup</> does not wait for + WAL segments to be archived so the backup process must ensure that all WAL + segments required for the backup are successfully archived. + </para> + </listitem> </orderedlist> </para> @@ -932,9 +942,9 @@ SELECT * FROM pg_stop_backup(false); <title>Making an exclusive low level backup</title> <para> The process for an exclusive backup is mostly the same as for a - non-exclusive one, but it differs in a few key steps. It does not allow - more than one concurrent backup to run, and there can be some issues on - the server if it crashes during the backup. Prior to PostgreSQL 9.6, this + non-exclusive one, but it differs in a few key steps. This type of backup + can only be taken on a primary and does not allow concurrent backups. + Prior to <productname>PostgreSQL</> 9.6, this was the only low-level method available, but it is now recommended that all users upgrade their scripts to use non-exclusive backups if possible. </para> @@ -992,6 +1002,11 @@ SELECT pg_start_backup('label', true); <xref linkend="backup-lowlevel-base-backup-data"> for things to consider during this backup. </para> + <para> + Note that if the server crashes during the backup it may not be + possible to restart until the <literal>backup_label</> file has been + manually deleted from the <envar>PGDATA</envar> directory. + </para> </listitem> <listitem> <para> diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 8482601294..01ebfb8d90 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -18070,11 +18070,22 @@ postgres=# select pg_start_backup('label_goes_here'); <function>pg_start_backup</>. In a non-exclusive backup, the contents of the <filename>backup_label</> and <filename>tablespace_map</> are returned in the result of the function, and should be written to files in the - backup (and not in the data directory). + backup (and not in the data directory). When executed on a primary + <function>pg_stop_backup</> will wait for WAL to be archived when archiving + is enabled. </para> <para> - The function also creates a backup history file in the transaction log + On a standby <function>pg_stop_backup</> will return immediately without + waiting so it's important to verify that all required WAL segments have been + archived. If write activity on the primary is low, it may be useful to run + <function>pg_switch_xlog</> on the primary in order to trigger an immediate + segment switch of the last required WAL. + </para> + + <para> + When executed on a primary, the function also creates a backup history file + in the write-ahead log archive area. The history file includes the label given to <function>pg_start_backup</>, the starting and ending transaction log locations for the backup, and the starting and ending times of the backup. The return
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