From: Tom Lane <tgl@sss.pgh.pa.us>
To: Holger Jakobs <holger@jakobs.com>
cc: pgsql-admin@lists.postgresql.org, rajeshkumar.dba09@gmail.com
Subject: Re: Pg_dump
In-reply-to: <404a126a-6229-7d83-9b86-70304a5693bc@jakobs.com>
References: 
 <CAJk5AtZX23PBG4rfrVt6cp3z_pYGtEE5JvvCRG6Lj3F7=1+C2Q@mail.gmail.com>
 <404a126a-6229-7d83-9b86-70304a5693bc@jakobs.com>
Comments: In-reply-to Holger Jakobs <holger@jakobs.com>
	message dated "Thu, 07 Dec 2023 19:13:40 +0100"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <1300347.1701975169.1@sss.pgh.pa.us>
Date: Thu, 07 Dec 2023 13:52:49 -0500
Message-ID: <1300348.1701975169@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/1300348.1701975169%40sss.pgh.pa.us>
Precedence: bulk

Holger Jakobs <holger@jakobs.com> writes:
> Am 07.12.23 um 19:11 schrieb Rajesh Kumar:
>> Will pg_dump cause blocking queries? If so how to take dump without 
>> blocking?

> Readers don't block writers, writers don't block readers in PostgreSQL.
> pg_dump is a reader.

To enlarge on that a bit: pg_dump takes AccessShareLock on every
table it intends to dump.  This does not conflict with ordinary
DML updates.  It *will* conflict with anything that wants
AccessExclusiveLock, which typically is schema-altering DDL.
See

https://www.postgresql.org/docs/current/explicit-locking.html#LOCKING-TABLES

So the answer to your question is "don't try to alter the
database schema while pg_dump is running".  You can alter
database content freely, though.

			regards, tom lane