Re: Query on partitioned table needs memory n_partitions * work_mem

From: Dimitrios Apostolou <jimis(at)gmx(dot)net>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: David Rowley <dgrowleyml(at)gmail(dot)com>, pgsql-general(at)lists(dot)postgresql(dot)org
Subject: Re: Query on partitioned table needs memory n_partitions * work_mem
Date: 2024-07-11 15:19:42
Message-ID: 82476a55-bb26-b566-e6d9-907592ce732e@gmx.net
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On Thu, 11 Jul 2024, Tom Lane wrote:

> Dimitrios Apostolou <jimis(at)gmx(dot)net> writes:
>> The TABLE test_runs_raw has 1000 partitions on RANGE(workitem_n).
>
> So don't do that. Adding partitions is not cost-free.
>

I understand that, they also add an administrative cost that I'd rather
avoid. But I ended up adding all these partitions because of performance
issues on a multi-billion rows table. There is probably some message from
me on this list a couple of years ago.

At the moment I have a work-around. I'm thankful that everyone is willing
to provide workarounds to all potential issues/bugs I have presented, but
unfortunately workarounds are not fixes, one will hit the same wall again
at some point.

My current concern is **reporting my findings responsibly**. I want to
provide as much data needed to pinpoint the issue, so that the developers
know exactly what's going on. Having right data is half the fix.

A way to track the issue would be nice. I might revisit it and even try to
submit a patch. I wonder how the postgres development community is
tracking all these issues, I've even started forgetting the ones I have
found, and I'm sure I have previously reported (on this list) a couple of
should-be-easy issues that would be ideal for beginners.

Regards,
Dimitris

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