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base repository: postgresql-cfbot/postgresql
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  • 2 commits
  • 9 files changed
  • 3 contributors

Commits on Apr 8, 2025

  1. Speedup child EquivalenceMember lookup in planner 

    When planning queries to partitioned tables, we create child
EquivalenceMembers for each EquivalenceMembers which mentions the parent
partitioned table.  For partitioned tables with large numbers of
partitions, this meant we could end up with many EquivalenceMembers and
this could cause the planner to become slow due to the linear lookups
that are performed on the EquivalenceClass ec_members's List.
Effectively, the more partitions which were present, the more lookups
needed to be performed for operations such as
find_ec_member_matching_expr() during create_plan() and the more
partitions present, the longer these searches would take.

To fix this, here we adjust how we store EquivalenceMembers for
em_is_child members.  Instead of storing these directly in ec_members,
these are now stored in a new array of Lists in the EquivalenceClass
which is indexed by the relid.  When we want to find EquivalenceMembers
belonging to a certain child relation, we can narrow the search to the
array element for that relation.

To make EquivalenceMember lookup easier and to reduce the amount of code
change, this commit provides a pair of functions to allow iteration over
the EquivalenceMembers in a class which handles finding the child
members, if required.  Callers that never need to look at child members
can remain using the foreach loop over ec_members, which will now often
be faster due to only parent-level members being stored there.

The actual performance increases here are highly dependent on the number
of partitions and the query being planned.  Performance increase can be
visible with as few as 8 partitions, but the speedup is marginal for
such low numbers of partitions.  The speedups become much more visible
with a few dozen to hundreds of partitions.  Some tested queries were
around 3x faster with 256 partitions.  For users with thousands of
partitions, these are likely to become significantly faster.  Some
testing has shown planner speedups of 20x or more.

Author: Yuya Watari <[email protected]>
Co-authored-by: David Rowley <[email protected]>
Reviewed-by: David Rowley <[email protected]>
Reviewed-by: Tom Lane <[email protected]>
Reviewed-by: Andrey Lepikhov <[email protected]>
Reviewed-by: Alena Rybakina <[email protected]>
Reviewed-by: Dmitry Dolgov <[email protected]>
Reviewed-by: Amit Langote <[email protected]>
Tested-by: Thom Brown <[email protected]>
Tested-by: Ashutosh Bapat <[email protected]>
Tested-by: newtglobal postgresql_contributors <[email protected]>
Discussion: https://postgr.es/m/CAJ2pMkZNCgoUKSE%2B_5LthD%2BKbXKvq6h2hQN8Esxpxd%2Bcxmgomg%40mail.gmail.com
    @proprowataya
    2 people authored and Commitfest Bot committed Apr 8, 2025
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  2. [CF 3701] v42 - Reducing planning time when tables have many partitions 

    This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/3701

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/CAApHDvpf+2rUi3rOepS9jMjiS3ezH9VcZisS+A+Ob5G5YpBZxg@mail.gmail.com
Author(s): Yuya Watari
    Commitfest Bot committed Apr 8, 2025
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