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  • 3 commits
  • 7 files changed
  • 2 contributors

Commits on Apr 3, 2025

  1. Add assertion to verify derived clause has constant RHS 

    find_derived_clause_for_ec_member() searches for a previously-derived
clause that equates a non-constant EquivalenceMember to a constant.
It is only called for EquivalenceClasses with ec_has_const set, and
with a non-constant member the EquivalenceMember to search for.

The matched clause is expected to have the non-constant member on the
left-hand side and the constant EquivalenceMember on the right.

Assert that the RHS is indeed a constant, to catch violations of this
structure and enforce assumptions made by
generate_base_implied_equalities_const().

Author: Ashutosh Bapat <[email protected]>
Discussion: https://postgr.es/m/CAExHW5scMxyFRqOFE6ODmBiW2rnVBEmeEcA-p4W_CyuEikURdA@mail.gmail.com
    @amitlan
    amitlan authored and Commitfest Bot committed Apr 3, 2025
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  2. Make derived clause lookup in EquivalenceClass more efficient 

    Derived clauses are stored in ec_derives, a List of RestrictInfos.
These clauses are later looked up by matching the left and right
EquivalenceMembers along with the clause's parent EC.

This linear search becomes expensive in queries with many joins or
partitions, where ec_derives may contain thousands of entries. In
particular, create_join_clause() can spend significant time scanning
this list.

To improve performance, introduce a hash table (ec_derives_hash) that
is built when the list reaches 32 entries -- the same threshold used
for join_rel_hash. The original list is retained alongside the hash
table to support EC merging and serialization
(_outEquivalenceClass()).

Each clause is stored in the hash table using a canonicalized key: the
EquivalenceMember with the lower memory address is placed in the key
before the one with the higher memory address. This avoids storing or
searching for both permutations of the same clause. For clauses
involving a constant EM, the key places NULL in the first slot and the
non-constant EM in the second.

The hash table is initialized using list_length(ec_derives_list) as
the size hint. simplehash internally adjusts this to the next power of
two after dividing by the fillfactor, so this typically results in at
least 64 buckets near the threshold -- avoiding immediate resizing
while adapting to the actual number of entries.

The lookup logic for derived clauses is now centralized in
ec_search_derived_clause_for_ems(), which consults the hash table when
available and falls back to the list otherwise.

The new ec_clear_derived_clauses() always frees ec_derives_list, even
though some of the original code paths that cleared the old
ec_derives field did not. This ensures consistent cleanup and avoids
leaking memory when large lists are discarded.

An assertion originally placed in find_derived_clause_for_ec_member()
is moved into ec_search_derived_clause_for_ems() so that it is
enforced consistently, regardless of whether the hash table or list is
used for lookup.

This design incorporates suggestions by David Rowley, who proposed
both the key canonicalization and the initial sizing approach to
balance memory usage and CPU efficiency.

Author: Ashutosh Bapat <[email protected]>
Reviewed-by: Amit Langote <[email protected]>
Reviewed-by: David Rowley <[email protected]>
Tested-by: Dmitry Dolgov <[email protected]>
Tested-by: Alvaro Herrera <[email protected]>
Tested-by: Amit Langote <[email protected]>
Tested-by: David Rowley <[email protected]>
Discussion: https://postgr.es/m/CAExHW5vZiQtWU6moszLP5iZ8gLX_ZAUbgEX0DxGLx9PGWCtqUg@mail.gmail.com
    @amitlan
    amitlan authored and Commitfest Bot committed Apr 3, 2025
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  3. [CF 4564] v9 - Reducing memory consumed by RestrictInfo list translat… 

    …ions in partitionwise join planning

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

https://commitfest.postgresql.org/patch/4564

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/CA+HiwqH8OaVD8LOpON=h3UyzXBwj=hHzTF_46DGvoeXzRrkx9A@mail.gmail.com
Author(s): Ashutosh Bapat
    Commitfest Bot committed Apr 3, 2025
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