Missing docs: setting up replication slots for standbys

On 09/03/2014 10:43 PM, Josh Berkus wrote:

Section 46.2.2 has this:

Note: PostgreSQL also has streaming replication slots (see Section
25.2.5), but they are used somewhat differently there.

Section 25.2.5 has this:

You can avoid this by setting wal_keep_segments to a value large enough
to ensure that WAL segments are not recycled too early, or by
configuring a replication slot for the standby.

... however, absolutely nowhere is it explained how to configure a
replication slot for a streaming replica. Is it, in fact, possible to
do so?

Searching ... it is possible. However, the way to do so is actually
scattered among 5 different doc pages. I'm not sure that I'm up for the
surgery required to make this make sense to users ... anybody else have
the energy/time?

The relevant pages in the docs are these:

http://www.postgresql.org/docs/9.4/static/standby-settings.html
http://www.postgresql.org/docs/9.4/static/functions-admin.html#FUNCTIONS-REPLICATION
http://www.postgresql.org/docs/9.4/static/logicaldecoding-explanation.html#AEN66111
http://www.postgresql.org/docs/9.4/static/warm-standby.html#STREAMING-REPLICATION

... otherwise, I'll just write a blog or postgresguide or something.

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On 2014-09-03 22:43:19 -0700, Josh Berkus wrote:

Section 46.2.2 has this:

Note: PostgreSQL also has streaming replication slots (see Section
25.2.5), but they are used somewhat differently there.

Section 25.2.5 has this:

You can avoid this by setting wal_keep_segments to a value large enough
to ensure that WAL segments are not recycled too early, or by
configuring a replication slot for the standby.

... however, absolutely nowhere is it explained how to configure a
replication slot for a streaming replica. Is it, in fact, possible to
do so?

It actually is explained. I don't have a built source handy right now,
so chapter numbers... But at least the following is there:

<sect3 id="streaming-replication-slots-config">
<title>Configuration Example</title>
<para>
You can create a replication slot like this:
<programlisting>
postgres=# SELECT * FROM pg_create_physical_replication_slot('node_a_slot');
slot_name | xlog_position
-------------+---------------
node_a_slot |

postgres=# SELECT * FROM pg_replication_slots;
slot_name | slot_type | datoid | database | active | xmin | restart_lsn
-------------+-----------+--------+----------+--------+------+-------------
node_a_slot | physical | | | f | |
(1 row)
</programlisting>
To configure the standby to use this slot, <varname>primary_slot_name</>
should be configured in the standby's <filename>recovery.conf</>.
Here is a simple example:
<programlisting>
standby_mode = 'on'
primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
primary_slot_name = 'node_a_slot'
</programlisting>

and I'm pretty sure primary_slot_name and such is configured at the
appropriate place too.

That's not to say it can't be be expanded and/or better linked...

Greetings,

Andres Freund

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On 09/03/2014 11:03 PM, Andres Freund wrote:

It actually is explained. I don't have a built source handy right now,
so chapter numbers... But at least the following is there:

<sect3 id="streaming-replication-slots-config">
<title>Configuration Example</title>
<para>
You can create a replication slot like this:
<programlisting>
postgres=# SELECT * FROM pg_create_physical_replication_slot('node_a_slot');
slot_name | xlog_position
-------------+---------------
node_a_slot |

postgres=# SELECT * FROM pg_replication_slots;
slot_name | slot_type | datoid | database | active | xmin | restart_lsn
-------------+-----------+--------+----------+--------+------+-------------
node_a_slot | physical | | | f | |
(1 row)
</programlisting>
To configure the standby to use this slot, <varname>primary_slot_name</>
should be configured in the standby's <filename>recovery.conf</>.
Here is a simple example:
<programlisting>
standby_mode = 'on'
primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
primary_slot_name = 'node_a_slot'
</programlisting>

and I'm pretty sure primary_slot_name and such is configured at the
appropriate place too.

Huh. I can't seem to find any way to navigate to that page. What is it
supposed to be under?

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Josh Berkus
PostgreSQL Experts Inc.
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On Thu, Sep 4, 2014 at 3:06 PM, Josh Berkus <josh@agliodbs.com> wrote:

On 09/03/2014 11:03 PM, Andres Freund wrote:

and I'm pretty sure primary_slot_name and such is configured at the
appropriate place too.

Huh. I can't seem to find any way to navigate to that page. What is it
supposed to be under?

Category seems adapted:
Chapter 25. High Availability, Load Balancing, and Replication
25.2. Log-Shipping Standby Servers
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Michael

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