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help / color / mirror / Atom feedFrom: Thomas Munro <[email protected]>
To: [email protected]
Subject: pgsql: Fix read_stream.c for changing io_combine_limit.
Date: Thu, 13 Mar 2025 03:00:35 +0000
Message-ID: <[email protected]> (raw)
Fix read_stream.c for changing io_combine_limit.
In a couple of places, read_stream.c assumed that io_combine_limit would
be stable during the lifetime of a stream. That is not true in at least
one unusual case: streams held by CURSORs where you could change the GUC
between FETCH commands, with unpredictable results.
Fix, by storing stream->io_combine_limit and referring only to that
after construction. This mirrors the treatment of the other important
setting {effective,maintenance}_io_concurrency, which is stored in
stream->max_ios.
One of the cases was the queue overflow space, which was sized for
io_combine_limit and could be overrun if the GUC was increased. Since
that coding was a little hard to follow, also introduce a variable for
better readability instead of open-coding the arithmetic. Doing so
revealed an off-by-one thinko while clamping max_pinned_buffers to
INT16_MAX, though that wasn't a live bug due to the current limits on
GUC values.
Back-patch to 17.
Discussion: https://postgr.es/m/CA%2BhUKG%2B2T9p-%2BzM6Eeou-RAJjTML6eit1qn26f9twznX59qtCA%40mail.gmail.com
Branch
------
REL_17_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/e273468070ab4212b0babb5b6e94cb57256c3512
Modified Files
--------------
src/backend/storage/aio/read_stream.c | 38 +++++++++++++++++++++++++----------
1 file changed, 27 insertions(+), 11 deletions(-)
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Subject: Re: pgsql: Fix read_stream.c for changing io_combine_limit.
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