Date: Thu, 3 Dec 2020 09:36:12 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Ravikumar Reddy <urravikumarreddy@gmail.com>
Cc: Atul Kumar <akumar14871@gmail.com>,
	pgsql-performance <pgsql-performance@lists.postgresql.org>
Subject: Re: time taking deletion on large tables
Message-ID: <20201203153612.GM24052@telsasoft.com>
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On Thu, Dec 03, 2020 at 08:43:57PM +0530, Ravikumar Reddy wrote:
> Please try the code below. Execute all the statements in one transaction.
> 
> select * into new_table from old_table where type = 'abcz';
> truncate table   old_table;
> inesrt into  old_table select * from new_table;

This looks like advice for when most of the rows are being deleted, but I don't
think that's true here.  It'd need to LOCK old_table, first, right?  Also,
truncate isn't MVCC safe.

Atul: What server version?  Do you have an index on feed_definition_id ?
https://wiki.postgresql.org/wiki/Slow_Query_Questions

If explain (analyze,buffers) SELECT runs in a reasonable time for that query,
include its output.

On Thu, Dec 3, 2020 at 8:16 PM Atul Kumar <akumar14871@gmail.com> wrote:
> The feed_posts table has over 50 Million rows.
>
> When I m deleting all rows of a certain type that are over 60 days old.
>
> When I try to do a delete like this:  it hangs for an entire day, so I
> need to kill it with pg_terminate_backend(pid).
>
> DELETE FROM feed_posts
> WHERE feed_definition_id = 'bf33573d-936e-4e55-8607-72b685d2cbae'
> AND created_at > '2020-05-11 00:00:00'
> AND created_at < '2020-05-12 00:00:00';
>
> So– I need help in figuring out how to do large deletes on a
> production database during normal hours.
>
> please help me on deleting the rows, Do I need to anything in postgres
> configuration ?
> or in table structure ?