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Add ALTER SUBSCRIPTION ... SKIP.

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This feature allows skipping the transaction on subscriber nodes.

If incoming change violates any constraint, logical replication stops
until it's resolved. Currently, users need to either manually resolve the
conflict by updating a subscriber-side database or by using function
pg_replication_origin_advance() to skip the conflicting transaction. This
commit introduces a simpler way to skip the conflicting transactions.

The user can specify LSN by ALTER SUBSCRIPTION ... SKIP (lsn = XXX),
which allows the apply worker to skip the transaction finished at
specified LSN. The apply worker skips all data modification changes within
the transaction.

Author: Masahiko Sawada
Reviewed-by: Takamichi Osumi, Hou Zhijie, Peter Eisentraut, Amit Kapila, Shi Yu, Vignesh C, Greg Nancarrow, Haiying Tang, Euler Taveira
Discussion: https://postgr.es/m/CAD21AoDeScrsHhLyEPYqN3sydg6PxAPVBboK=30xJfUVihNZDA@mail.gmail.com
This commit is contained in:
Amit Kapila
2022-03-22 07:11:19 +05:30
parent 315ae75e9b
commit 208c5d65bb
18 changed files with 665 additions and 173 deletions
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10
doc/src/sgml/catalogs.sgml
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@ -7797,6 +7797,16 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>subskiplsn</structfield> <type>pg_lsn</type>
</para>
<para>
Finish LSN of the transaction whose changes are to be skipped, if a valid
LSN; otherwise <literal>0/0</literal>.
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>subconninfo</structfield> <type>text</type>

27
doc/src/sgml/logical-replication.sgml
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@ -362,19 +362,24 @@ CONTEXT: processing remote data for replication origin "pg_16395" during "INSER
</screen>
The LSN of the transaction that contains the change violating the constraint and
the replication origin name can be found from the server log (LSN 0/14C0378 and
replication origin <literal>pg_16395</literal> in the above case). To skip the
transaction, the subscription needs to be disabled temporarily by
<command>ALTER SUBSCRIPTION ... DISABLE</command> first or alternatively, the
replication origin <literal>pg_16395</literal> in the above case). The
transaction that produces conflict can be skipped by using
<command>ALTER SUBSCRIPTION ... SKIP</command> with the finish LSN
(i.e., LSN 0/14C0378). The finish LSN could be an LSN at which the transaction
is committed or prepared on the publisher. Alternatively, the transaction can
also be skipped by calling the <link linkend="pg-replication-origin-advance">
<function>pg_replication_origin_advance()</function></link> function
transaction. Before using this function, the subscription needs to be disabled
temporarily either by <command>ALTER SUBSCRIPTION ... DISABLE</command> or, the
subscription can be used with the <literal>disable_on_error</literal> option.
Then, the transaction can be skipped by calling the
<link linkend="pg-replication-origin-advance">
<function>pg_replication_origin_advance()</function></link> function with
the <parameter>node_name</parameter> (i.e., <literal>pg_16395</literal>) and the
next LSN of the transaction's LSN (i.e., LSN 0/14C0379). After that the replication
can be resumed by <command>ALTER SUBSCRIPTION ... ENABLE</command>. The current
position of origins can be seen in the
<link linkend="view-pg-replication-origin-status">
Then, you can use <function>pg_replication_origin_advance()</function> function
with the <parameter>node_name</parameter> (i.e., <literal>pg_16395</literal>)
and the next LSN of the finish LSN (i.e., 0/14C0379). The current position of
origins can be seen in the <link linkend="view-pg-replication-origin-status">
<structname>pg_replication_origin_status</structname></link> system view.
Please note that skipping the whole transaction include skipping changes that
might not violate any constraint. This can easily make the subscriber
inconsistent.
</para>
</sect1>

42
doc/src/sgml/ref/alter_subscription.sgml
View File

@ -29,6 +29,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> REFRESH PUB
ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> ENABLE
ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> DISABLE
ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> SET ( <replaceable class="parameter">subscription_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] )
ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> SKIP ( <replaceable class="parameter">skip_option</replaceable> = <replaceable class="parameter">value</replaceable> )
ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> OWNER TO { <replaceable>new_owner</replaceable> | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <replaceable>new_name</replaceable>
</synopsis>
@ -210,6 +211,47 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
</listitem>
</varlistentry>
<varlistentry>
<term><literal>SKIP ( <replaceable class="parameter">skip_option</replaceable> = <replaceable class="parameter">value</replaceable> )</literal></term>
<listitem>
<para>
Skips applying all changes of the remote transaction. If incoming data
violates any constraints, logical replication will stop until it is
resolved. By using <command>ALTER SUBSCRIPTION ... SKIP</command> command,
the logical replication worker skips all data modification changes within
the transaction. This option has no effect on the transactions that are
already prepared by enabling <literal>two_phase</literal> on
subscriber.
After logical replication worker successfully skips the transaction or
finishes a transaction, LSN (stored in
<structname>pg_subscription</structname>.<structfield>subskiplsn</structfield>)
is cleared. See <xref linkend="logical-replication-conflicts"/> for
the details of logical replication conflicts. Using this command requires
superuser privilege.
</para>
<para>
<replaceable>skip_option</replaceable> specifies options for this operation.
The supported option is:
<variablelist>
<varlistentry>
<term><literal>lsn</literal> (<type>pg_lsn</type>)</term>
<listitem>
<para>
Specifies the finish LSN of the remote transaction whose changes
are to be skipped by the logical replication worker. The finish LSN
is the LSN at which the transaction is either committed or prepared.
Skipping individual subtransaction is not supported. Setting
<literal>NONE</literal> resets the LSN.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">new_owner</replaceable></term>
<listitem>