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Add support for prepared transactions to built-in logical replication.

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To add support for streaming transactions at prepare time into the
built-in logical replication, we need to do the following things:

* Modify the output plugin (pgoutput) to implement the new two-phase API
callbacks, by leveraging the extended replication protocol.

* Modify the replication apply worker, to properly handle two-phase
transactions by replaying them on prepare.

* Add a new SUBSCRIPTION option "two_phase" to allow users to enable
two-phase transactions. We enable the two_phase once the initial data sync
is over.

We however must explicitly disable replication of two-phase transactions
during replication slot creation, even if the plugin supports it. We
don't need to replicate the changes accumulated during this phase,
and moreover, we don't have a replication connection open so we don't know
where to send the data anyway.

The streaming option is not allowed with this new two_phase option. This
can be done as a separate patch.

We don't allow to toggle two_phase option of a subscription because it can
lead to an inconsistent replica. For the same reason, we don't allow to
refresh the publication once the two_phase is enabled for a subscription
unless copy_data option is false.

Author: Peter Smith, Ajin Cherian and Amit Kapila based on previous work by Nikhil Sontakke and Stas Kelvich
Reviewed-by: Amit Kapila, Sawada Masahiko, Vignesh C, Dilip Kumar, Takamichi Osumi, Greg Nancarrow
Tested-By: Haiying Tang
Discussion: https://postgr.es/m/02DA5F5E-CECE-4D9C-8B4B-418077E2C010@postgrespro.ru
Discussion: https://postgr.es/m/CAA4eK1+opiV4aFTmWWUF9h_32=HfPOW9vZASHarT0UA5oBrtGw@mail.gmail.com
This commit is contained in:
Amit Kapila
2021-07-14 07:33:50 +05:30
parent 6c9c283166
commit a8fd13cab0
43 changed files with 2382 additions and 191 deletions
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37
doc/src/sgml/ref/create_subscription.sgml
View File

@@ -237,6 +237,43 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
are fully decoded on the publisher, and only then sent to the
subscriber as a whole.
</para>
<para>
The <literal>streaming</literal> option cannot be used with the
<literal>two_phase</literal> option.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>two_phase</literal> (<type>boolean</type>)</term>
<listitem>
<para>
Specifies whether two-phase commit is enabled for this subscription.
The default is <literal>false</literal>.
</para>
<para>
When two-phase commit is enabled then the decoded transactions are sent
to the subscriber on the PREPARE TRANSACTION. By default, the transaction
prepared on the publisher is decoded as a normal transaction at commit.
</para>
<para>
The two-phase commit implementation requires that the replication has
successfully passed the initial table synchronization phase. This means
even when two_phase is enabled for the subscription, the internal
two-phase state remains temporarily "pending" until the initialization
phase is completed. See column
<literal>subtwophasestate</literal> of <xref linkend="catalog-pg-subscription"/>
to know the actual two-phase state.
</para>
<para>
The <literal>two_phase</literal> option cannot be used with the
<literal>streaming</literal> option.
</para>
</listitem>
</varlistentry>
</variablelist></para>