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From: Tom Lane <[email protected]>
To: Holger Jakobs <[email protected]>
Cc: [email protected]
Cc: [email protected]
Subject: Re: Pg_dump
Date: Thu, 07 Dec 2023 13:52:49 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CAJk5AtZX23PBG4rfrVt6cp3z_pYGtEE5JvvCRG6Lj3F7=1+C2Q@mail.gmail.com>
	<[email protected]>

Holger Jakobs <[email protected]> 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

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