On 10/20/14 2:07 PM, Peter Eisentraut wrote:
> The reference page for pg_receivexlog
> (http://www.postgresql.org/docs/9.4/static/app-pgreceivexlog.html) has
> this note:
>
> """
> When using pg_receivexlog instead of archive_command, the server will
> continue to recycle transaction log files even if the backups are not
> properly archived, since there is no command that fails. This can be
> worked around by having an archive_command that fails when the file has
> not been properly archived yet, for example:
>
> archive_command = 'sleep 5 && test -f /mnt/server/archivedir/%f'
> The initial timeout is necessary because pg_receivexlog works using
> asynchronous replication and can therefore be slightly behind the master.
> """
>
> ISTM that this should be replaced with something to the effect of, if
> you are using pg_receivexlog instead of archive_command, you had better
> use slots.
Here is a patch.
diff --git a/doc/src/sgml/ref/pg_receivexlog.sgml b/doc/src/sgml/ref/pg_receivexlog.sgml
index 2ab392e..f90b61c 100644
--- a/doc/src/sgml/ref/pg_receivexlog.sgml
+++ b/doc/src/sgml/ref/pg_receivexlog.sgml
@@ -324,17 +324,12 @@ <title>Notes</title>
<para>
When using <application>pg_receivexlog</application> instead of
- <xref linkend="guc-archive-command">, the server will continue to
- recycle transaction log files even if the backups are not properly
- archived, since there is no command that fails. This can be worked
- around by having an <xref linkend="guc-archive-command"> that fails
- when the file has not been properly archived yet, for example:
-<programlisting>
-archive_command = 'sleep 5 && test -f /mnt/server/archivedir/%f'
-</programlisting>
- The initial timeout is necessary because
- <application>pg_receivexlog</application> works using asynchronous
- replication and can therefore be slightly behind the master.
+ <xref linkend="guc-archive-command"> as the main WAL backup method, it is
+ strongly recommended to use replication slots. Otherwise, the server is
+ free to recycle or remove transaction log files before they are backed up,
+ because it does not have any information, either
+ from <xref linkend="guc-archive-command"> or the replication slots, about
+ how far the WAL stream has been archived.
</para>
</refsect1>
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