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From: Joe Conway <[email protected]>
To: Frits Hoogland <[email protected]>
Cc: Priya V <[email protected]>
Cc: [email protected]
Subject: Re: Safe vm.overcommit_ratio for Large Multi-Instance PostgreSQL Fleet
Date: Wed, 6 Aug 2025 21:12:41 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>

On 8/6/25 17:14, Frits Hoogland wrote:
>> As I said, do not disable swap. You don't need a huge amount, but
>> maybe 16 GB or so would do it.

> Joe, please, can you state a technical reason for saying this?
> All you are saying is ‘don’t do this’.
> 
> I’ve stated my reasons for why this doesn’t make sense, and you don’t give any reason.

What do you call the below?

>> Op 6 aug 2025 om 18:33 heeft Joe Conway <[email protected]> het volgende geschreven:

>> * Swap is what is used when anonymous memory must be reclaimed to
>> allow for an allocation of anonymous memory.
>> 
>> * The Linux kernel will aggressively use all available memory for
>> file buffers, pushing usage against the limits.
>> 
>> * Especially in the older 4 series kernels, file buffers often
>> cannot be reclaimed fast enough
>> 
>> * With no swap and a large-ish anonymous memory request, it is
>> easy to push over the limit to cause the OOM killer to strike.
>> 
>> * On the other hand, with swap enabled anon memory can be
>> reclaimed giving the kernel more time to deal with file buffer
>> reclamation.
>> 
>> At least that is what I have observed.

If you don't think that is adequate technical reason, feel free to 
ignore my advice.

-- 
Joe Conway
PostgreSQL Contributors Team
Amazon Web Services: https://aws.amazon.com

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