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help / color / mirror / Atom feedFrom: Andres Freund <[email protected]>
To: [email protected]
Subject: pgsql: Remove HeapBitmapScan's skip_fetch optimization
Date: Wed, 02 Apr 2025 19:35:39 +0000
Message-ID: <[email protected]> (raw)
Remove HeapBitmapScan's skip_fetch optimization
The optimization does not take the removal of TIDs by a concurrent vacuum into
account. The concurrent vacuum can remove dead TIDs and make pages ALL_VISIBLE
while those dead TIDs are referenced in the bitmap. This can lead to a
skip_fetch scan returning too many tuples.
It likely would be possible to implement this optimization safely, but we
don't have the necessary infrastructure in place. Nor is it clear that it's
worth building that infrastructure, given how limited the skip_fetch
optimization is.
In the backbranches we just disable the optimization by always passing
need_tuples=true to table_beginscan_bm(). We can't perform API/ABI changes in
the backbranches and we want to make the change as minimal as possible.
Author: Matthias van de Meent <[email protected]>
Reported-By: Konstantin Knizhnik <[email protected]>
Discussion: https://postgr.es/m/CAEze2Wg3gXXZTr6_rwC+s4-o2ZVFB5F985uUSgJTsECx6AmGcQ@mail.gmail.com
Backpatch-through: 13
Branch
------
REL_16_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/980727b84107f88cecfd4b94fe80269d948633c4
Modified Files
--------------
src/backend/executor/nodeBitmapHeapscan.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
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Subject: Re: pgsql: Remove HeapBitmapScan's skip_fetch optimization
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