Horton

MergeAppend could consider sorting cheapest child path

Alexander Pyhalov <a.pyhalov@postgrespro.ru>

View thread
From: Alexander Pyhalov <a.pyhalov@postgrespro.ru>
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-06-18T16:45:09Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Mostly-cosmetic adjustments to estimate_multivariate_bucketsize().

  2. Consider fractional paths in generate_orderedappend_paths

Attachments

Hi.

Now when planner finds suitable pathkeys in 
generate_orderedappend_paths(), it uses them, even if explicit sort of 
the cheapest child path could be more efficient.

We encountered this issue on partitioned table with two indexes, where 
one is suitable for sorting, and another is good for selecting data. 
MergeAppend was generated
with subpaths doing index scan on suitably ordered index and filtering a 
lot of data.
The suggested fix allows MergeAppend to consider sorting on cheapest 
childrel total path as an alternative.

-- 
Best regards,
Alexander Pyhalov,
Postgres Professional