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