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Allow logical decoding via the walsender interface.

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In order for this to work, walsenders need the optional ability to
connect to a database, so the "replication" keyword now allows true
or false, for backward-compatibility, and the new value "database"
(which causes the "dbname" parameter to be respected).

walsender needs to loop not only when idle but also when sending
decoded data to the user and when waiting for more xlog data to decode.
This means that there are now three separate loops inside walsender.c;
although some refactoring has been done here, this is still a bit ugly.

Andres Freund, with contributions from Álvaro Herrera, and further
review by me.
This commit is contained in:
Robert Haas
2014-03-10 13:50:28 -04:00
parent cb9a0c7987
commit 5a991ef869
12 changed files with 915 additions and 167 deletions
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24
doc/src/sgml/protocol.sgml
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@ -1302,10 +1302,13 @@
<para>
To initiate streaming replication, the frontend sends the
<literal>replication</> parameter in the startup message. This tells the
backend to go into walsender mode, wherein a small set of replication commands
can be issued instead of SQL statements. Only the simple query protocol can be
used in walsender mode.
<literal>replication</> parameter in the startup message. A boolean value
of <literal>true</> tells the backend to go into walsender mode, wherein a
small set of replication commands can be issued instead of SQL statements. Only
the simple query protocol can be used in walsender mode.
Passing <literal>database</> as the value instructs walsender to connect to
the database specified in the <literal>dbname</> parameter, which will allow
the connection to be used for logical replication from that database.
The commands accepted in walsender mode are:
@ -1315,7 +1318,7 @@ The commands accepted in walsender mode are:
<listitem>
<para>
Requests the server to identify itself. Server replies with a result
set of a single row, containing three fields:
set of a single row, containing four fields:
</para>
<para>
@ -1357,6 +1360,17 @@ The commands accepted in walsender mode are:
</listitem>
</varlistentry>
<varlistentry>
<term>
dbname
</term>
<listitem>
<para>
Database connected to or NULL.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</listitem>