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From: Andres Freund <[email protected]>
To: Justin Pryzby <[email protected]>
Cc: Don Seiler <[email protected]>
Cc: P C <[email protected]>
Cc: Magnus Hagander <[email protected]>
Cc: Julien Rouhaud <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: [email protected]
Subject: Re: Estimating HugePages Requirements?
Date: Mon, 9 Aug 2021 20:38:32 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
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Hi,

On 2021-08-09 18:58:53 -0500, Justin Pryzby wrote:
> Define shared_buffers as the exact size to be allocated/requested from the OS
> (regardless of whether they're huge pages or not), and have postgres compute
> everything else based on that.  So shared_buffers=2GB would end up being 1950MB
> (or so) of buffer cache.  We'd have to check that after the other allocations,
> there's still at least 128kB left for the buffer cache.  Maybe we'd have to
> bump the minimum value of shared_buffers.

I don't like that. How much "other" shared memory we're going to need is
very hard to predict and depends on extensions, configuration options
like max_locks_per_transaction, max_connections to a significant
degree. This way the user ends up needing to guess at least as much as
before to get to a sensible shared_buffers.

Greetings,

Andres Freund





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