in <xref linkend="functions-replication-table"> are for
controlling and interacting with replication features.
See <xref linkend="streaming-replication">,
- <xref linkend="streaming-replication-slots">, <xref linkend="replication-origins">
+ <xref linkend="streaming-replication-slots">, and
+ <xref linkend="replication-origins">
for information about the underlying features. Use of these
functions is restricted to superusers.
</para>
</para>
<para>
- The functions described in <xref linkend="functions-snapshot-synchronization">, <xref
- linkend="functions-recovery-control">, and <xref
- linkend="functions-admin-backup"> are also relevant for replication.
+ The functions described in
+ <xref linkend="functions-admin-backup">,
+ <xref linkend="functions-recovery-control">, and
+ <xref linkend="functions-snapshot-synchronization">
+ are also relevant for replication.
</para>
<table id="functions-replication-table">
<literal><function>pg_replication_origin_create(<parameter>node_name</parameter> <type>text</type>)</function></literal>
</entry>
<entry>
- <parameter>internal_id</parameter> <type>oid</type>
+ <type>oid</type>
</entry>
<entry>
- Create a replication origin with the passed in external
- name, and create an internal id for it.
+ Create a replication origin with the given external
+ name, and return the internal id assigned to it.
</entry>
</row>
void
</entry>
<entry>
- Delete a previously created replication origin, including the
+ Delete a previously created replication origin, including any
associated replay progress.
</entry>
</row>
<literal><function>pg_replication_origin_oid(<parameter>node_name</parameter> <type>text</type>)</function></literal>
</entry>
<entry>
- <parameter>internal_id</parameter> <type>oid</type>
+ <type>oid</type>
</entry>
<entry>
- Lookup replication origin by name and return the internal id. If no
+ Lookup a replication origin by name and return the internal id. If no
corresponding replication origin is found an error is thrown.
</entry>
</row>
void
</entry>
<entry>
- Configure the current session to be replaying from the passed in
+ Mark the current session as replaying from the given
origin, allowing replay progress to be tracked. Use
<function>pg_replication_origin_session_reset</function> to revert.
Can only be used if no previous origin is configured.
<literal><function>pg_replication_origin_session_is_setup()</function></literal>
</entry>
<entry>
- bool
+ <type>bool</type>
</entry>
<entry>
Has a replication origin been configured in the current session?
<literal><function>pg_replication_origin_session_progress(<parameter>flush</parameter> <type>bool</type>)</function></literal>
</entry>
<entry>
- pg_lsn
+ <type>pg_lsn</type>
</entry>
<entry>
Return the replay position for the replication origin configured in
void
</entry>
<entry>
- Mark the current transaction to be replaying a transaction that has
- committed at the passed in <acronym>LSN</acronym> and timestamp. Can
+ Mark the current transaction as replaying a transaction that has
+ committed at the given <acronym>LSN</acronym> and timestamp. Can
only be called when a replication origin has previously been
configured using
<function>pg_replication_origin_session_setup()</function>.
void
</entry>
<entry>
- Set replication progress for the passed in node to the passed in
+ Set replication progress for the given node to the given
position. This primarily is useful for setting up the initial position
or a new position after configuration changes and similar. Be aware
that careless use of this function can lead to inconsistently
<literal><function>pg_replication_origin_progress(<parameter>node_name</parameter> <type>text</type>, <parameter>flush</parameter> <type>bool</type>)</function></literal>
</entry>
<entry>
- pg_lsn
+ <type>pg_lsn</type>
</entry>
<entry>
- Return the replay position for the passed in replication origin. The
+ Return the replay position for the given replication origin. The
parameter <parameter>flush</parameter> determines whether the
corresponding local transaction will be guaranteed to have been
flushed to disk or not.
<!-- doc/src/sgml/replication-origins.sgml -->
<chapter id="replication-origins">
<title>Replication Progress Tracking</title>
+
<indexterm zone="replication-origins">
<primary>Replication Progress Tracking</primary>
</indexterm>
<para>
Replication origins are intended to make it easier to implement
logical replication solutions on top
- of <xref linkend="logicaldecoding">. They provide a solution to two
- common problems:
+ of <link linkend="logicaldecoding">logical decoding</link>.
+ They provide a solution to two common problems:
<itemizedlist>
- <listitem><para>How to safely keep track of replication progress</para></listitem>
- <listitem><para>How to change replication behavior, based on the
- origin of a row; e.g. to avoid loops in bi-directional replication
- setups</para></listitem>
+ <listitem>
+ <para>How to safely keep track of replication progress</para>
+ </listitem>
+ <listitem>
+ <para>How to change replication behavior based on the
+ origin of a row; for example, to prevent loops in bi-directional
+ replication setups</para>
+ </listitem>
</itemizedlist>
</para>
<para>
- Replication origins consist out of a name and an <type>oid</type>. The name,
+ Replication origins have just two properties, a name and an OID. The name,
which is what should be used to refer to the origin across systems, is
free-form <type>text</type>. It should be used in a way that makes conflicts
between replication origins created by different replication solutions
unlikely; e.g. by prefixing the replication solution's name to it.
- The <type>oid</type> is used only to avoid having to store the long version
+ The OID is used only to avoid having to store the long version
in situations where space efficiency is important. It should never be shared
- between systems.
+ across systems.
</para>
<para>
- Replication origins can be created using the
+ Replication origins can be created using the function
<link linkend="pg-replication-origin-create"><function>pg_replication_origin_create()</function></link>;
dropped using
<link linkend="pg-replication-origin-drop"><function>pg_replication_origin_drop()</function></link>;
and seen in the
<link linkend="catalog-pg-replication-origin"><structname>pg_replication_origin</structname></link>
- catalog.
+ system catalog.
</para>
<para>
- When replicating from one system to another (independent of the fact that
- those two might be in the same cluster, or even same database) one
- nontrivial part of building a replication solution is to keep track of
+ One nontrivial part of building a replication solution is to keep track of
replay progress in a safe manner. When the applying process, or the whole
cluster, dies, it needs to be possible to find out up to where data has
- successfully been replicated. Naive solutions to this like updating a row in
- a table for every replayed transaction have problems like run-time overhead
- bloat.
+ successfully been replicated. Naive solutions to this, such as updating a
+ row in a table for every replayed transaction, have problems like run-time
+ overhead and database bloat.
</para>
<para>
</para>
<para>
- In more complex replication topologies than replication from exactly one
- system to one other, another problem can be that it is hard to avoid
+ In replication topologies more complex than replication from exactly one
+ system to one other system, another problem can be that it is hard to avoid
replicating replayed rows again. That can lead both to cycles in the
replication and inefficiencies. Replication origins provide an optional
mechanism to recognize and prevent that. When configured using the functions
referenced in the previous paragraph, every change and transaction passed to
output plugin callbacks (see <xref linkend="logicaldecoding-output-plugin">)
generated by the session is tagged with the replication origin of the
- generating session. This allows to treat them differently in the output
- plugin, e.g. ignoring all but locally originating rows. Additionally
+ generating session. This allows treating them differently in the output
+ plugin, e.g. ignoring all but locally-originating rows. Additionally
the <link linkend="logicaldecoding-output-plugin-filter-origin">
<function>filter_by_origin_cb</function></link> callback can be used
to filter the logical decoding change stream based on the
source. While less flexible, filtering via that callback is
- considerably more efficient.
+ considerably more efficient than doing it in the output plugin.
</para>
</chapter>