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Doc: Fix the mistakes in the subscription's failover option.

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The documentation incorrectly stated that users could not alter the
subscription's failover option when the two-phase commit is enabled.

The steps to confirm that the standby server is ready for failover were
incorrect.

Author: Shveta Malik, Hou Zhijie
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/OS0PR01MB571657B72F8D75BD858DCCE394AD2@OS0PR01MB5716.jpnprd01.prod.outlook.com
Discussion: https://postgr.es/m/CAJpy0uBBk+OZXXqQ00Gai09XR+mDi2=9sMBYY0F+BedoFivaMA@mail.gmail.com
This commit is contained in:
Amit Kapila 2024-07-24 14:24:45 +05:30
parent f6bef362ca
commit 07fbecb87b
2 changed files with 44 additions and 24 deletions
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61
doc/src/sgml/logical-replication.sgml
View File

@ -725,32 +725,45 @@ ALTER SUBSCRIPTION
<procedure>
<step performance="required">
<para>
On the subscriber node, use the following SQL to identify which slots
should be synced to the standby that we plan to promote. This query will
return the relevant replication slots, including the main slots and table
synchronization slots associated with the failover-enabled subscriptions.
Note that the table sync slot should be synced to the standby server only
if the table copy is finished (See <xref linkend="catalog-pg-subscription-rel"/>).
On the subscriber node, use the following SQL to identify which replication
slots should be synced to the standby that we plan to promote. This query
will return the relevant replication slots associated with the
failover-enabled subscriptions.
<programlisting>
test_sub=# SELECT
array_agg(quote_literal(s.subslotname)) AS slots
FROM pg_subscription s
WHERE s.subfailover AND
s.subslotname IS NOT NULL;
slots
-------
{'sub1','sub2','sub3'}
(1 row)
</programlisting></para>
</step>
<step performance="required">
<para>
On the subscriber node, use the following SQL to identify which table
synchronization slots should be synced to the standby that we plan to promote.
This query needs to be run on each database that includes the failover-enabled
subscription(s). Note that the table sync slot should be synced to the standby
server only if the table copy is finished
(See <xref linkend="catalog-pg-subscription-rel"/>).
We don't need to ensure that the table sync slots are synced in other scenarios
as they will either be dropped or re-created on the new primary server in those
cases.
<programlisting>
test_sub=# SELECT
array_agg(slot_name) AS slots
array_agg(quote_literal(slot_name)) AS slots
FROM
((
SELECT r.srsubid AS subid, CONCAT('pg_', srsubid, '_sync_', srrelid, '_', ctl.system_identifier) AS slot_name
(
SELECT CONCAT('pg_', srsubid, '_sync_', srrelid, '_', ctl.system_identifier) AS slot_name
FROM pg_control_system() ctl, pg_subscription_rel r, pg_subscription s
WHERE r.srsubstate = 'f' AND s.oid = r.srsubid AND s.subfailover
) UNION (
SELECT s.oid AS subid, s.subslotname as slot_name
FROM pg_subscription s
WHERE s.subfailover
))
WHERE slot_name IS NOT NULL;
);
slots
-------
{sub1,sub2,sub3}
{'pg_16394_sync_16385_7394666715149055164'}
(1 row)
</programlisting></para>
</step>
@ -761,13 +774,15 @@ test_sub=# SELECT
<programlisting>
test_standby=# SELECT slot_name, (synced AND NOT temporary AND NOT conflicting) AS failover_ready
FROM pg_replication_slots
WHERE slot_name IN ('sub1','sub2','sub3');
slot_name | failover_ready
-------------+----------------
sub1 | t
sub2 | t
sub3 | t
(3 rows)
WHERE slot_name IN
('sub1','sub2','sub3', 'pg_16394_sync_16385_7394666715149055164');
slot_name | failover_ready
--------------------------------------------+----------------
sub1 | t
sub2 | t
sub3 | t
pg_16394_sync_16385_7394666715149055164 | t
(4 rows)
</programlisting></para>
</step>
</procedure>

7
doc/src/sgml/ref/alter_subscription.sgml
View File

@ -72,8 +72,13 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
<command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
<command>ALTER SUBSCRIPTION ... SET (two_phase = false)</command>
cannot be executed inside a transaction block.
</para>
These commands also cannot be executed when the subscription has
<para>
Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command> and
<command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
with <literal>refresh</literal> option as <literal>true</literal> also cannot
be executed when the subscription has
<link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
commit enabled, unless
<link linkend="sql-createsubscription-params-with-copy-data"><literal>copy_data</literal></link>