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

Commits on Mar 4, 2025

  1. Show index search count in EXPLAIN ANALYZE. 

    Expose the count of index searches/index descents in EXPLAIN ANALYZE's
output for index scan nodes.  This information is particularly useful
with scans that use ScalarArrayOp quals, where the number of index scans
isn't predictable in advance (at least not with optimizations like the
one added to nbtree by Postgres 17 commit 5bf748b).  It will also be
useful when EXPLAIN ANALYZE shows details of an nbtree index scan that
uses skip scan optimizations set to be introduced by an upcoming patch.

The instrumentation works by teaching index AMs to increment a new
nsearches counter whenever a new index search begins.  The counter is
incremented at exactly the same point that index AMs must already
increment the index's pg_stat_*_indexes.idx_scan counter (since we're
counting exactly the same event, though at a finer granularity).

There was much debate on the best place to store the new counter.  We
settled on storing it in the index scan descriptor (IndexScanDescData).
This approach is unique among all the different approaches used to track
query execution costs, but the requirements seem to leave us with no
better alternative.  The requirements are themselves unique (at least
right now): we must track the number of searches at the scan granularity
(at the level of the scan, not the level of the system/relation), from
within each index AM's amgettuple/amgetbitmap routine (since it isn't
possible to track it from the executor proper).

Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Tomas Vondra <tomas@vondra.me>
Reviewed-By: Robert Haas <robertmhaas@gmail.com>
Reviewed-By: Masahiro Ikeda <ikedamsh@oss.nttdata.com>
Discussion: https://postgr.es/m/CAH2-Wz=PKR6rB7qbx+Vnd7eqeB5VTcrW=iJvAsTsKbdG+kW_UA@mail.gmail.com
Discussion: https://postgr.es/m/CAH2-WzkRqvaqR2CTNqTZP0z6FuL4-3ED6eQB0yx38XBNj1v-4Q@mail.gmail.com
    @petergeoghegan
    petergeoghegan authored and Commitfest Bot committed Mar 4, 2025
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  2. [CF 5183] Showing primitive index scan count in EXPLAIN ANALYZE (for … 

    …skip scan and SAOP scans)

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

https://commitfest.postgresql.org/patch/5183

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/CAH2-Wz=zzD+752xD8NjVfdxh6c_vRdhWhwRHSw4qXOt=quk=vg@mail.gmail.com
Author(s): Peter Geoghegan
    Commitfest Bot committed Mar 4, 2025
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