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Doc: Update information about manually creating slots.

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There are some cases (e.g. when the subscription is created using the
connect = false option) where the remote replication slot was not created
automatically and the user must create it manually before the subscription
can be activated. There was not enough information in the docs for users
to do this easily.

Author: Peter Smith
Reviewd by: Shi yu, Amit Kapila
Discussion: https://postgr.es/m/CAHut+PvqdqOanheWSHDyhQiF+Z-7w=-+k4U+bwbT=b6YQ_hrXQ@mail.gmail.com
This commit is contained in:
Amit Kapila 2022-11-02 11:40:37 +05:30
parent 568546f7e4
commit 155601de7f
2 changed files with 179 additions and 14 deletions
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159
doc/src/sgml/logical-replication.sgml
View File

@ -320,7 +320,7 @@
</sect2>
<sect2 id="logical-replication-subscription-examples">
<title>Examples</title>
<title>Examples - Setup Logical Replication</title>
<para>
Create some test tables on the publisher.
@ -512,6 +512,163 @@ test_sub=# SELECT * FROM t3;
</programlisting></para>
</sect2>
<sect2 id="logical-replication-subscription-examples-deferred-slot">
<title>Examples - Deferred Replication Slot Creation</title>
<para>
There are some cases (e.g.
<xref linkend="logical-replication-subscription-slot"/>) where, if the
remote replication slot was not created automatically, the user must create
it manually before the subscription can be activated. The steps to create
the slot and activate the subscription are shown in the following examples.
These examples specify the standard logical decoding plugin
(<literal>pgoutput</literal>), which is what the built-in logical
replication uses.
</para>
<para>
First, create a publication for the examples to use.
<programlisting>
test_pub=# CREATE PUBLICATION pub1 FOR ALL TABLES;
CREATE PUBLICATION
</programlisting></para>
<para>
Example 1: Where the subscription says <literal>connect = false</literal>
</para>
<para>
<itemizedlist>
<listitem>
<para>
Create the subscription.
<programlisting>
test_sub=# CREATE SUBSCRIPTION sub1
test_sub-# CONNECTION 'host=localhost dbname=test_pub'
test_sub-# PUBLICATION pub1
test_sub-# WITH (connect=false);
WARNING: subscription was created, but is not connected
HINT: To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
CREATE SUBSCRIPTION
</programlisting></para>
</listitem>
<listitem>
<para>
On the publisher, manually create a slot. Because the name was not
specified during <literal>CREATE SUBSCRIPTION</literal>, the name of the
slot to create is same as the subscription name, e.g. "sub1".
<programlisting>
test_pub=# SELECT * FROM pg_create_logical_replication_slot('sub1', 'pgoutput');
slot_name | lsn
-----------+-----------
sub1 | 0/19404D0
(1 row)
</programlisting></para>
</listitem>
<listitem>
<para>
On the subscriber, complete the activation of the subscription. After
this the tables of <literal>pub1</literal> will start replicating.
<programlisting>
test_sub=# ALTER SUBSCRIPTION sub1 ENABLE;
ALTER SUBSCRIPTION
test_sub=# ALTER SUBSCRIPTION sub1 REFRESH PUBLICATION;
ALTER SUBSCRIPTION
</programlisting></para>
</listitem>
</itemizedlist>
</para>
<para>
Example 2: Where the subscription says <literal>connect = false</literal>,
but also specifies the <literal>slot_name</literal>
<itemizedlist>
<listitem>
<para>
Create the subscription.
<programlisting>
test_sub=# CREATE SUBSCRIPTION sub1
test_sub-# CONNECTION 'host=localhost dbname=test_pub'
test_sub-# PUBLICATION pub1
test_sub-# WITH (connect=false, slot_name='myslot');
WARNING: subscription was created, but is not connected
HINT: To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
CREATE SUBSCRIPTION
</programlisting></para>
</listitem>
<listitem>
<para>
On the publisher, manually create a slot using the same name that was
specified during <literal>CREATE SUBSCRIPTION</literal>, e.g. "myslot".
<programlisting>
test_pub=# SELECT * FROM pg_create_logical_replication_slot('myslot', 'pgoutput');
slot_name | lsn
-----------+-----------
myslot | 0/19059A0
(1 row)
</programlisting></para>
</listitem>
<listitem>
<para>
On the subscriber, the remaining subscription activation steps are the
same as before.
<programlisting>
test_sub=# ALTER SUBSCRIPTION sub1 ENABLE;
ALTER SUBSCRIPTION
test_sub=# ALTER SUBSCRIPTION sub1 REFRESH PUBLICATION;
ALTER SUBSCRIPTION
</programlisting></para>
</listitem>
</itemizedlist>
</para>
<para>
Example 3: Where the subscription specifies <literal>slot_name = NONE</literal>
<itemizedlist>
<listitem>
<para>
Create the subscription. When <literal>slot_name = NONE</literal> then
<literal>enabled = false</literal>, and
<literal>create_slot = false</literal> are also needed.
<programlisting>
test_sub=# CREATE SUBSCRIPTION sub1
test_sub-# CONNECTION 'host=localhost dbname=test_pub'
test_sub-# PUBLICATION pub1
test_sub-# WITH (slot_name=NONE, enabled=false, create_slot=false);
CREATE SUBSCRIPTION
</programlisting></para>
</listitem>
<listitem>
<para>
On the publisher, manually create a slot using any name, e.g. "myslot".
<programlisting>
test_pub=# SELECT * FROM pg_create_logical_replication_slot('myslot', 'pgoutput');
slot_name | lsn
-----------+-----------
myslot | 0/1905930
(1 row)
</programlisting></para>
</listitem>
<listitem>
<para>
On the subscriber, associate the subscription with the slot name just
created.
<programlisting>
test_sub=# ALTER SUBSCRIPTION sub1 SET (slot_name='myslot');
ALTER SUBSCRIPTION
</programlisting></para>
</listitem>
<listitem>
<para>
The remaining subscription activation steps are same as before.
<programlisting>
test_sub=# ALTER SUBSCRIPTION sub1 ENABLE;
ALTER SUBSCRIPTION
test_sub=# ALTER SUBSCRIPTION sub1 REFRESH PUBLICATION;
ALTER SUBSCRIPTION
</programlisting></para>
</listitem>
</itemizedlist>
</para>
</sect2>
</sect1>
<sect1 id="logical-replication-row-filter">

34
doc/src/sgml/ref/create_subscription.sgml
View File

@ -120,11 +120,11 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
<para>
Since no connection is made when this option is
<literal>false</literal>, no tables are subscribed, and so
after you enable the subscription nothing will be replicated.
You will need to then run
<literal>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</literal>
for tables to be subscribed.
<literal>false</literal>, no tables are subscribed. To initiate
replication, you must manually create the replication slot, enable
the subscription, and refresh the subscription. See
<xref linkend="logical-replication-subscription-examples-deferred-slot"/>
for examples.
</para>
</listitem>
</varlistentry>
@ -135,8 +135,12 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
<para>
Specifies whether the command should create the replication slot on
the publisher. The default is <literal>true</literal>.
</para>
<para>
If set to <literal>false</literal>, you are responsible for
creating the publisher's slot in some other way.
creating the publisher's slot in some other way. See
<xref linkend="logical-replication-subscription-examples-deferred-slot"/>
for examples.
</para>
</listitem>
</varlistentry>
@ -162,11 +166,13 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
<para>
Setting <literal>slot_name</literal> to <literal>NONE</literal>
means there will be no replication slot
associated with the subscription. Use this when you will be
creating the replication slot later manually. Such
subscriptions must also have both <literal>enabled</literal> and
<literal>create_slot</literal> set to <literal>false</literal>.
means there will be no replication slot associated with the
subscription. Such subscriptions must also have both
<literal>enabled</literal> and <literal>create_slot</literal> set to
<literal>false</literal>. Use this when you will be creating the
replication slot later manually. See
<xref linkend="logical-replication-subscription-examples-deferred-slot"/>
for examples.
</para>
</listitem>
</varlistentry>
@ -357,8 +363,10 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
replication slot separately (using the
function <function>pg_create_logical_replication_slot</function> with the
plugin name <literal>pgoutput</literal>) and create the subscription using
the parameter <literal>create_slot = false</literal>. This is an
implementation restriction that might be lifted in a future release.
the parameter <literal>create_slot = false</literal>. See
<xref linkend="logical-replication-subscription-examples-deferred-slot"/>
for examples. This is an implementation restriction that might be lifted in a
future release.
</para>
<para>