On 8/18/17 3:00 PM, Robert Haas wrote:
>
> If you update the patch I'll apply it to 11 and 10.
Attached is the updated patch.
I didn't like the vague "there can be some issues on the server if it
crashes during the backup" so I added a new paragraph at the appropriate
step to give a more detailed explanation of the problem.
Thanks,
--
-David
da...@pgmasters.net
diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml
index 0e7c6e2051..76f81975f1 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, true);
</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_wal</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>
@@ -908,9 +911,12 @@ SELECT * FROM pg_stop_backup(false, true);
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 and
the
+ <literal>wait_for_archive</> parameter is <literal>true</>,
<function>pg_stop_backup</> does not return until the last segment has
been archived.
+ On a standby, <varname>archive_mode</> must be <literal>always</> in order
+ for <function>pg_stop_backup</> to wait.
Archiving of these files happens automatically since you have
already configured <varname>archive_command</>. In most cases this
happens quickly, but you are advised to monitor your archive
@@ -943,9 +949,9 @@ SELECT * FROM pg_stop_backup(false, true);
<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 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>
@@ -1003,6 +1009,11 @@ SELECT pg_start_backup('label', true);
<xref linkend="backup-lowlevel-base-backup-data"> for things to
consider during this backup.
</para>
+ <para>
+ Note well 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 PGDATA directory.
+ </para>
</listitem>
<listitem>
<para>
@@ -1012,15 +1023,10 @@ SELECT pg_start_backup('label', true);
<programlisting>
SELECT pg_stop_backup();
</programlisting>
- This function, when called on a primary, terminates the backup mode and
+ This function terminates backup mode and
performs an automatic switch to the next WAL segment. The reason for the
switch is to arrange for the last WAL segment written during the backup
- interval to be ready to archive. When called on a standby, this function
- only terminates backup mode. A subsequent WAL segment switch will be
- needed in order to ensure that all WAL files needed to restore the backup
- can be archived; if the primary does not have sufficient write activity
- to trigger one, <function>pg_switch_wal</function> should be executed on
- the primary.
+ interval to be ready to archive.
</para>
</listitem>
<listitem>
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index b43ec30a4e..28eda97273 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -18606,7 +18606,8 @@ postgres=# select pg_start_backup('label_goes_here');
</para>
<para>
- The function also creates a backup history file in the write-ahead log
+ 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 write-ahead log
locations for
the backup, and the starting and ending times of the backup. The return
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