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Small streaming replication document improvements. Be more explicit that

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it's asynchronous.
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Heikki Linnakangas 2010-02-25 08:57:47 +00:00
parent cd2b7d3c4d
commit 7c6c09c039
1 changed files with 23 additions and 18 deletions
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doc/src/sgml/high-availability.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.49 2010/02/22 11:47:30 heikki Exp $ --> <!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.50 2010/02/25 08:57:47 heikki Exp $ -->
<chapter id="high-availability"> <chapter id="high-availability">
<title>High Availability, Load Balancing, and Replication</title> <title>High Availability, Load Balancing, and Replication</title>
@ -523,8 +523,8 @@ protocol to make nodes agree on a serializable transactional order.
<varname>archive_timeout</varname> parameter, which can be set as low <varname>archive_timeout</varname> parameter, which can be set as low
as a few seconds. However such a low setting will as a few seconds. However such a low setting will
substantially increase the bandwidth required for file shipping. substantially increase the bandwidth required for file shipping.
If you need a window of less than a minute or so, it is probably better If you need a window of less than a minute or so, consider using
to consider record-based log shipping. <xref linkend="streaming-replication">.
</para> </para>
<para> <para>
@ -762,19 +762,25 @@ if (!triggered)
</indexterm> </indexterm>
<para> <para>
<productname>PostgreSQL</> includes a simple streaming replication Streaming replication allows a standby server to stay more up-to-date
mechanism, which allows the standby server to stay more up-to-date than than is possible with file-based log shipping. The standby connects
file-based log shipping. The standby connects to the primary to the primary, which streams WAL records to the standby as they're
and the primary starts streaming WAL records from where the standby generated, without waiting for the WAL file to be filled.
left off, and continues streaming them as they are generated, without </para>
waiting for the WAL file to be filled. So with streaming replication,
<varname>archive_timeout</> does not need to be changed to reduce <para>
possible data loss. Streaming replication is asynchronous, so there is stilll a small delay
between committing a transaction in the primary and for the changes to
become visible in the standby. The delay is however much smaller than with
file-based log shipping, typically under one second assuming the standby
is powerful enough to keep up with the load. With streaming replication,
<varname>archive_timeout</> is not required to reduce the data loss
window.
</para> </para>
<para> <para>
Streaming replication relies on file-based continuous archiving for Streaming replication relies on file-based continuous archiving for
making the base backup and for allowing a standby to catch up if it is making the base backup and for allowing the standby to catch up if it is
disconnected from the primary for long enough for the primary to disconnected from the primary for long enough for the primary to
delete old WAL files still required by the standby. delete old WAL files still required by the standby.
</para> </para>
@ -796,11 +802,10 @@ if (!triggered)
<listitem> <listitem>
<para> <para>
Set up continuous archiving from the primary to a WAL archive located Set up continuous archiving from the primary to a WAL archive located
in a directory on the standby server. Ensure that in a directory on the standby server. In particular, set
<xref linkend="guc-archive-mode">, <xref linkend="guc-archive-mode"> and
<xref linkend="guc-archive-command"> and <xref linkend="guc-archive-command">
<xref linkend="guc-archive-timeout"> to archive WAL files in a location accessible from the standby
are set appropriately on the primary
(see <xref linkend="backup-archiving-wal">). (see <xref linkend="backup-archiving-wal">).
</para> </para>
</listitem> </listitem>
@ -808,7 +813,7 @@ if (!triggered)
<listitem> <listitem>
<para> <para>
Set <xref linkend="guc-listen-addresses"> and authentication options Set <xref linkend="guc-listen-addresses"> and authentication options
(see <filename>pg_hba.conf</>) so the standby server can connect to (see <filename>pg_hba.conf</>) on the primary so that the standby server can connect to
the <literal>replication</> pseudo-database on the primary server (see the <literal>replication</> pseudo-database on the primary server (see
<xref linkend="streaming-replication-authentication">). <xref linkend="streaming-replication-authentication">).
</para> </para>