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Send status updates back from standby server to master, indicating how far

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the standby has written, flushed, and applied the WAL. At the moment, this
is for informational purposes only, the values are only shown in
pg_stat_replication system view, but in the future they will also be needed
for synchronous replication.

Extracted from Simon riggs' synchronous replication patch by Robert Haas, with
some tweaking by me.
This commit is contained in:
Heikki Linnakangas
2011-02-10 21:00:29 +02:00
parent 4c468b37a2
commit b186523fd9
15 changed files with 352 additions and 22 deletions
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23
doc/src/sgml/config.sgml
View File

@ -1984,6 +1984,29 @@ SET ENABLE_SEQSCAN TO OFF;
</listitem>
</varlistentry>
<varlistentry id="guc-wal-receiver-status-interval" xreflabel="wal_receiver_status_interval">
<term><varname>wal_receiver_status_interval</varname> (<type>integer</type>)</term>
<indexterm>
<primary><varname>wal_receiver_status_interval</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
Specifies the minimum frequency, in seconds, for the WAL receiver
process on the standby to send information about replication progress
to the primary, where they can be seen using the
<literal>pg_stat_replication</literal> view. The standby will report
the last transaction log position it has written, the last position it
has flushed to disk, and the last position it has applied. Updates are
sent each time the write or flush positions changed, or at least as
often as specified by this parameter. Thus, the apply position may
lag slightly behind the true position. Setting this parameter to zero
disables status updates completely. This parameter can only be set in
the <filename>postgresql.conf</> file or on the server command line.
The default value is 10 seconds.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-vacuum-defer-cleanup-age" xreflabel="vacuum_defer_cleanup_age">
<term><varname>vacuum_defer_cleanup_age</varname> (<type>integer</type>)</term>
<indexterm>

7
doc/src/sgml/monitoring.sgml
View File

@ -298,8 +298,11 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
<entry><structname>pg_stat_replication</><indexterm><primary>pg_stat_replication</primary></indexterm></entry>
<entry>One row per WAL sender process, showing process <acronym>ID</>,
user OID, user name, application name, client's address and port number,
time at which the server process began execution, current WAL sender
state and transaction log location. The columns detailing what exactly
time at which the server process began execution, and the current WAL
sender state and transaction log location. In addition, the standby
reports the last transaction log position it received and wrote, the last
position it flushed to disk, and the last position it replayed, and this
information is also displayed here. The columns detailing what exactly
the connection is doing are only visible if the user examining the view
is a superuser.
</entry>

76
doc/src/sgml/protocol.sgml
View File

@ -1469,6 +1469,82 @@ The commands accepted in walsender mode are:
shutdown), it will send a CommandComplete message before exiting.
This might not happen during an abnormal shutdown, of course.
</para>
<para>
The receiving process can send a status update back to the sender at
any time, using the following message format (also in the payload of
a CopyData message):
</para>
<para>
<variablelist>
<varlistentry>
<term>
Standby status update (F)
</term>
<listitem>
<para>
<variablelist>
<varlistentry>
<term>
Byte1('r')
</term>
<listitem>
<para>
Identifies the message as a receiver status update.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
Byte8
</term>
<listitem>
<para>
The location of the last WAL byte + 1 received and written to disk
in the standby, in XLogRecPtr format.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
Byte8
</term>
<listitem>
<para>
The location of the last WAL byte + 1 flushed to disk in
the standby, in XLogRecPtr format.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
Byte8
</term>
<listitem>
<para>
The location of the last WAL byte + 1 applied in the standby, in
XLogRecPtr format.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
Byte8
</term>
<listitem>
<para>
The server's system clock at the time of transmission,
given in TimestampTz format.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</listitem>
</varlistentry>