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doc: Clarify some things on pg_receivexlog reference page

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Peter Eisentraut 2015-11-19 14:19:04 -05:00
parent bb8b179603
commit 04f5622b63
1 changed files with 25 additions and 10 deletions
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doc/src/sgml/ref/pg_receivexlog.sgml
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@ -31,7 +31,7 @@ PostgreSQL documentation
Description Description
</title> </title>
<para> <para>
<application>pg_receivexlog</application> is used to stream transaction log <application>pg_receivexlog</application> is used to stream the transaction log
from a running <productname>PostgreSQL</productname> cluster. The transaction from a running <productname>PostgreSQL</productname> cluster. The transaction
log is streamed using the streaming replication protocol, and is written log is streamed using the streaming replication protocol, and is written
to a local directory of files. This directory can be used as the archive to a local directory of files. This directory can be used as the archive
@ -49,19 +49,19 @@ PostgreSQL documentation
</para> </para>
<para> <para>
Unlike the standby's WAL receiver, <application>pg_receivexlog</> Unlike the WAL receiver of a PostgreSQL standby server, <application>pg_receivexlog</>
by default flushes WAL data only when a WAL file is closed. by default flushes WAL data only when a WAL file is closed.
<literal>--synchronous</> option must be specified to flush WAL data The option <option>--synchronous</> must be specified to flush WAL data
in real time and ensure it's safely flushed to disk. in real time.
</para> </para>
<para> <para>
The transaction log is streamed over a regular The transaction log is streamed over a regular
<productname>PostgreSQL</productname> connection, and uses the replication <productname>PostgreSQL</productname> connection and uses the replication
protocol. The connection must be made with a superuser or a user protocol. The connection must be made with a superuser or a user
having <literal>REPLICATION</literal> permissions (see having <literal>REPLICATION</literal> permissions (see
<xref linkend="role-attributes">), and <filename>pg_hba.conf</filename> <xref linkend="role-attributes">), and <filename>pg_hba.conf</filename>
must explicitly permit the replication connection. The server must also be must permit the replication connection. The server must also be
configured with <xref linkend="guc-max-wal-senders"> set high enough to configured with <xref linkend="guc-max-wal-senders"> set high enough to
leave at least one session available for the stream. leave at least one session available for the stream.
</para> </para>
@ -137,10 +137,18 @@ PostgreSQL documentation
When this option is used, <application>pg_receivexlog</> will report When this option is used, <application>pg_receivexlog</> will report
a flush position to the server, indicating when each segment has been a flush position to the server, indicating when each segment has been
synchronized to disk so that the server can remove that segment if it synchronized to disk so that the server can remove that segment if it
is not otherwise needed. <literal>--synchronous</literal> option must is not otherwise needed.
be specified when making <application>pg_receivexlog</> run as </para>
synchronous standby by using replication slot. Otherwise WAL data
cannot be flushed frequently enough for this to work correctly. <para>
When the replication client
of <application>pg_receivexlog</application> is configured on the
server as a synchronous standby, then using a replication slot will
report the flush position to the server, but only when a WAL file is
closed. Therefore, that configuration will cause transactions on the
primary to wait for a long time and effectively not work
satisfactorily. The option <literal>--synchronous</literal> (see
below) must be specified in addition to make this work correctly.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
@ -153,6 +161,13 @@ PostgreSQL documentation
send a status packet back to the server immediately after flushing, send a status packet back to the server immediately after flushing,
regardless of <literal>--status-interval</>. regardless of <literal>--status-interval</>.
</para> </para>
<para>
This option should be specified if the replication client
of <application>pg_receivexlog</application> is configured on the
server as a synchronous standby, to ensure that timely feedback is
sent to the server.
</para>
</listitem> </listitem>
</varlistentry> </varlistentry>