Re: Replication lag

From: Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
To: Wasim Devale <wasimd60(at)gmail(dot)com>, pgsql-admin <pgsql-admin(at)postgresql(dot)org>, Pgsql-admin <pgsql-admin(at)lists(dot)postgresql(dot)org>
Subject: Re: Replication lag
Date: 2025-05-23 09:46:48
Message-ID: 0903948da238870688d6a52bab616319947231c4.camel@cybertec.at
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On Fri, 2025-05-23 at 12:43 +0530, Wasim Devale wrote:
> Reply wal and query execution on replica can coexists?

Yes, you can have both.
But there is the possibility of replication conflicts, which can
either delay replay of the WAL or lead to cacneled queries on the
standby.

To see why this is unavoidable in some cases, consider the following
scenario:

- on the standby, there is a long-running query on table A
- on the primary, somebody executes "DROP TABLE A"

The change gets replicated to the standby, but it clearly cannot be
replayed while the query is still running.

Yours,
Laurenz Albe

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