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From: Laurenz Albe <[email protected]>
To: Abhishek Prakash <[email protected]>
To: [email protected] <[email protected]>
To: [email protected] <[email protected]>
To: [email protected] <[email protected]>
Subject: Re: ***Conflict with recovery error***
Date: Fri, 20 Jan 2023 10:55:48 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <SI2PR02MB5490F6959EF4B92A9CC41C2681C59@SI2PR02MB5490.apcprd02.prod.outlook.com>
References: <SI2PR02MB5490F6959EF4B92A9CC41C2681C59@SI2PR02MB5490.apcprd02.prod.outlook.com>

On Fri, 2023-01-20 at 08:56 +0000, Abhishek Prakash wrote:
> We are facing below issue with read replica we did work arounds by setting
> hot_standby_feedback, max_standby_streaming_delay and max_standby_archive_delay,
> which indeed caused adverse effects on primary DB and storage. As our DB is
> nearly 6 TB which runs as AWS Postgres RDS. 
>  
> Even the below error occurs on tables where vacuum is disabled and no DML
> operations are permitted. Will there be any chances to see row versions
> being changed even if vacuum is disabled.
> Please advise.
>  
> 2023-01-13 07:20:12 UTC:10.64.103.75(61096):ubpreplica@ubprdb01:[17707]:ERROR:  canceling statement due to conflict with recovery
> 2023-01-13 07:20:12 UTC:10.64.103.75(61096):ubpreplica@ubprdb01:[17707]:DETAIL:  User query might have needed to see row versions that must be removed.

It could be HOT chain pruning or an anti-wraparound autovacuum (which runs
even if autovacuum is disabled).
Disabling autovacuum is not a smart idea to begin with.

Your best bet is to set "max_standby_streaming_delay = -1".

More reading:
https://www.cybertec-postgresql.com/en/streaming-replication-conflicts-in-postgresql/

Yours,
Laurenz Albe

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