Starting with Pg – where/how can I set configuration parameters?

Previously I wrote about locating config files.

The thing is – postgresql.conf is not the only place you can set your configuration in.

In here, I'll describe all the places that can be used, why do we even have more than one place, and finally – how to find out where given value comes from.

Continue reading Starting with Pg – where/how can I set configuration parameters?

Starting with Pg – where is the config?

Over the years I saw some people find themselves in position where they have to start dealing with PostgreSQL with minimal, or none, prior exposure. This leads to problems with seemingly easy tasks – how to change config? How to find stuff in logs?

So I decided to write some blogposts to be able to point such people to pre-made tutorials.

And I start today, with information on how to find PostgreSQL config files.

Continue reading Starting with Pg – where is the config?

Waiting for PostgreSQL 14 – Add idle_session_timeout.

On 6th of January 2021, Tom Lane committed patch:

Add idle_session_timeout.
 
This GUC variable works much like idle_in_transaction_session_timeout,
in that it kills sessions that have waited too long for a new client
query.  But it applies when we're not in a transaction, rather than
when we are.
 
Li Japin, reviewed by David Johnston and Hayato Kuroda, some
fixes by me
 
Discussion: https://postgr.es/m/763A0689-F189-459E-946F-F0EC4458980B@hotmail.com

Continue reading Waiting for PostgreSQL 14 – Add idle_session_timeout.

How to limit rows to at most N per category – fix

A bit ago I wrote a blog post that was supposed to show how to keep number of rows in table to N per some category.

Unfortunately, I overlooked a problem related to concurrency.

Continue reading How to limit rows to at most N per category – fix

How to limit rows to at most N per category

The question was asked relatively recently on irc. And it proved to be non-trivial.

Surely, if you want to have one row per category (one address per user), it's trivial – add user_id column to addresses, make it unique, and we're done. But what if we want to allow five addresses? Or five thousands?

Let's see.

Continue reading How to limit rows to at most N per category

Waiting for PostgreSQL 14 – Rename wal_keep_segments to wal_keep_size.

On 20th of July 2020, Fujii Masao committed patch:

Rename wal_keep_segments to wal_keep_size.
 
max_slot_wal_keep_size that was added in v13 and wal_keep_segments are
the GUC parameters to specify how much WAL files to retain for
the standby servers. While max_slot_wal_keep_size accepts the number of
bytes of WAL files, wal_keep_segments accepts the number of WAL files.
This difference of setting units between those similar parameters could
be confusing to users.
 
To alleviate this situation, this commit renames wal_keep_segments to
wal_keep_size, and make users specify the WAL size in it instead of
the number of WAL files.
 
There was also the idea to rename max_slot_wal_keep_size to
max_slot_wal_keep_segments, in the discussion. But we have been moving
away from measuring in segments, for example, checkpoint_segments was
replaced by max_wal_size. So we concluded to rename wal_keep_segments
to wal_keep_size.
 
Back-patch to v13 where max_slot_wal_keep_size was added.
 
Author: Fujii Masao
Reviewed-by: Álvaro Herrera, Kyotaro Horiguchi, David Steele
Discussion: https://postgr.es/m/574b4ea3-e0f9-b175-ead2-ebea7faea855@oss.nttdata.com

Continue reading Waiting for PostgreSQL 14 – Rename wal_keep_segments to wal_keep_size.

Waiting for PostgreSQL 12 – Add SETTINGS option to EXPLAIN, to print modified settings.

On 3rd of April 2019, Tomas Vondra committed patch:

Add SETTINGS option to EXPLAIN, to print modified settings.
 
 
Query planning is affected by a number of configuration options, and it
may be crucial to know which of those options were set to non-default
values.  With this patch you can say EXPLAIN (SETTINGS ON) to include
that information in the query plan.  Only options affecting planning,
with values different from the built-in default are printed.
 
This patch also adds auto_explain.log_settings option, providing the
same capability in auto_explain module.
 
Author: Tomas Vondra
 
Discussion: https://postgr.es/m/e1791b4c-df9c-be02-edc5-7c8874944be0@2ndquadrant.com

Continue reading Waiting for PostgreSQL 12 – Add SETTINGS option to EXPLAIN, to print modified settings.

Waiting for PostgreSQL 12 – Add log_statement_sample_rate parameter

On 29th of November 2018, Alvaro Herrera committed patch:

Add log_statement_sample_rate parameter
 
This allows to set a lower log_min_duration_statement value without
incurring excessive log traffic (which reduces performance).  This can
be useful to analyze workloads with lots of short queries.
 
Author: Adrien Nayrat
 
Discussion: https://postgr.es/m/-ee1e-db9f-fa97-@anayrat.info

Continue reading Waiting for PostgreSQL 12 – Add log_statement_sample_rate parameter

Waiting for PostgreSQL 12 – Integrate recovery.conf into postgresql.conf

On 25th of November 2018, Peter Eisentraut committed patch:

Integrate recovery.conf into postgresql.conf
 
recovery.conf settings are now set in postgresql.conf (or other GUC
sources).  Currently, all the affected settings are PGC_POSTMASTER;
this could be refined in the future case by case.
 
Recovery is now initiated by a file recovery.signal.  Standby mode is
initiated by a file standby.signal.  The standby_mode setting is
gone.  If a recovery.conf file is found, an error is issued.
 
The trigger_file setting has been renamed to promote_trigger_file as
part of the move.
 
The documentation chapter "Recovery Configuration" has been integrated
into "Server Configuration".
 
pg_basebackup -R now appends settings to postgresql.auto.conf and
creates a standby.signal file.
 
Author: Fujii Masao
Author: Simon Riggs
Author: Abhijit Menon-Sen
Author: Sergei Kornilov
Discussion: https://www.postgresql.org/message-id/flat/@web3g.yandex.ru/

Continue reading Waiting for PostgreSQL 12 – Integrate recovery.conf into postgresql.conf