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From: Philip Semanchuk <[email protected]>
To: yudhi s <[email protected]>
Cc: pgsql-general <[email protected]>
Subject: Re: Suggestion for memory parameters
Date: Mon, 30 Sep 2024 11:16:20 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAEzWdqfUQuKtpqGAwf86dwkjPq2Kkeyj6Pw31GXr92YC8M2Y5g@mail.gmail.com>
References: <CAEzWdqfUQuKtpqGAwf86dwkjPq2Kkeyj6Pw31GXr92YC8M2Y5g@mail.gmail.com>



> On Sep 26, 2024, at 7:03 AM, yudhi s <[email protected]> wrote:
> 
> In a RDS postgres ...

>  Is it fine to let it use "FreeLocalStorage" unless it goes till zero?

Hi Yudhi,
FreeLocalStorage and some of the other things you ask about are specific to AWS RDS, so you might have better luck getting answers on an RDS-specific mailing list. We also use RDS-hosted Postgres and so I completely understand how Postgres and RDS are intertwined.

We have had runaway queries exhaust FreeLocalStorage. It has been quite a while since that happened, so my memories are hazy, but I’m pretty sure that when we used all of FreeLocalStorage, the result was that Postgres restarted. It might be equivalent to using all memory and disk space on a standalone system. Once there’s no storage left, behavior is unpredictable but we can’t be surprised if things crash. Usually our runaway queries got killed before FreeLocalStorage filled up, but not always.

I second Veem’s suggestion to set work_mem on a per-session basis. Also note that the doc for work_mem says, “the total memory used could be many times the value of work_mem; it is necessary to keep this fact in mind when choosing the value."

https://www.postgresql.org/docs/current/runtime-config-resource.html#GUC-WORK-MEM

Cheers
Philip

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