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help / color / mirror / Atom feedFrom: Melanie Plageman <[email protected]>
To: Andres Freund <[email protected]>
Cc: Alexander Lakhin <[email protected]>
Cc: Tomas Vondra <[email protected]>
Cc: David Rowley <[email protected]>
Cc: Kirill Reshke <[email protected]>
Cc: Chao Li <[email protected]>
Cc: Andrey Borodin <[email protected]>
Cc: Xuneng Zhou <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Subject: Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access)
Date: Thu, 16 Apr 2026 16:21:35 -0400
Message-ID: <CAAKRu_a_t6yHc94K6WkjUg_bDgXSK33LAYNACZFg-3RjrPPMcw@mail.gmail.com> (raw)
In-Reply-To: <yemtvnnnj4c6ehsmv6cu2x7h5i3nentpoeuqdtmyp3lnrw7ydu@7uwd2pogt5nv>
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On Sun, Apr 5, 2026 at 11:49 AM Andres Freund <[email protected]> wrote:
>
> I think we should probably just have GetLocalPinLimit() return something
> considerably smaller than num_temp_buffers, e.g. num_temp_buffers / 4 or
> so.
I think num_temp_buffers / 4 seems reasonable for GetLocalPinLimit().
We'd also need to make this change in GetAdditionalLocalPinLimit().
Making this change fixes the specific case Alexander pointed out.
We will likely see an impact on performance impact because this will
keep the readahead distance substantially lower for temp table cases
with only one read stream.
> There always may be more than one scan going on, so we can't ever promise that
> there's at least a certain number of pins available. The main goal of the
> shared pin limit is to prevent one backend from pinning disproportionally much
> of s_b. And for that eventually scaling down to just needing 1-2 pins per
> scan is sufficient.
With the last sentence "And for that eventually scaling down to just
needing 1-2 pins per scan is sufficient." -- how do you mean to relate
that to what we will do with local buffers case?
- Melanie
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Subject: Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access)
In-Reply-To: <CAAKRu_a_t6yHc94K6WkjUg_bDgXSK33LAYNACZFg-3RjrPPMcw@mail.gmail.com>
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