pg.ddx.io pgsql-hackers@postgresql.org mailing list archive help / color / mirror / Atom feed From: Yuhang Qiu <iamqyh@gmail.com>
To: Palak Chaturvedi <chaturvedipalak1911@gmail.com>
Cc: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Cc: pgsql-hackers@postgresql.org, Heikki Linnakangas <heikki.linnakangas@databricks.com>
Cc: Haoyu Huang <haoyu.huang@databricks.com>
Cc: Tomas Vondra <tomas@vondra.me>
Cc: Peter Eisentraut <peter@eisentraut.org>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Jakub Wartak <jakub.wartak@enterprisedb.com>
Subject: Re: Changing shared_buffers without restart
Date: Fri, 11 Sep 2026 18:56:28 +0800
Message-ID: <8E7D0939-ADE1-405A-91D2-0139A6E322B3@gmail.com> (raw )
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Hi Palak,
> Yes. v20260908-0016 rechecks BM_TAG_VALID under LockBufHdr() and does
> UnlockBufHdr() + continue instead of asserting when the tag was
> cleared concurrently.
>
> Right, that line predates the MADV_REMOVE range fix. Removed it in
> v20260908-0015.
Thanks. 0015 and 0016 LGTM.
I also tested the patches and did some more review.
With shared_buffers=32MB and max_shared_buffers left at its default, parallel
workers fail to start, even without any resize:
FATAL: failed to initialize shared_buffers to 16384
CONTEXT: parallel worker
RestoreGUCState() resets the GUC to its 128MB boot value, which exceeds
MaxNBuffers and fails the check hook.
There is also a performance issue in the grow path:
PGSharedMemoryEnsureAllocated() gets the whole structure's range, rather than
just the added range. Even a small increase makes MADV_POPULATE_WRITE walk the
existing range again, adding overhead for large buffer pools. Could we limit
this to the page-aligned [current_end, new_end), as in the shrink path?
Two minor points:
* check_shared_buffers() allows equality with MaxNBuffers, so "must be less than"
should be "must not exceed".
* In proc.c, "specifid there" should be "specified there".
Some issues raised in earlier reviews remain unaddressed. Could you include a
status list with the next update, separating resolved and unresolved items?
That would help reviewers who are new to the thread or haven't followed it for
a while.
Best regards,
Yuhang Qiu
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To: pgsql-hackers@postgresql.org
Cc: iamqyh@gmail.com, chaturvedipalak1911@gmail.com, ashutosh.bapat.oss@gmail.com, heikki.linnakangas@databricks.com, haoyu.huang@databricks.com, tomas@vondra.me, peter@eisentraut.org, thomas.munro@gmail.com, 9erthalion6@gmail.com, robertmhaas@gmail.com, andres@anarazel.de, jakub.wartak@enterprisedb.com
Subject: Re: Changing shared_buffers without restart
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