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author | Tom Lane <tgl@sss.pgh.pa.us> | 2019-05-22 11:46:57 -0400 |
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committer | Tom Lane <tgl@sss.pgh.pa.us> | 2019-05-22 11:47:02 -0400 |
commit | 166f69f769c83ef8759d905bf7f1a9aa1d97a340 (patch) | |
tree | e4e7dcc6de3e1bac0007126c42451fb1e0cef169 /src/backend/access/gist/gistproc.c | |
parent | 728840fe13acff7b03a4b1a813eeb8900ce5e469 (diff) | |
download | postgresql-166f69f769c83ef8759d905bf7f1a9aa1d97a340.tar.gz |
Fix O(N^2) performance issue in pg_publication_tables view.
The original coding of this view relied on a correlated IN sub-query.
Our planner is not very bright about correlated sub-queries, and even
if it were, there's no way for it to know that the output of
pg_get_publication_tables() is duplicate-free, making the de-duplicating
semantics of IN unnecessary. Hence, rewrite as a LATERAL sub-query.
This provides circa 100X speedup for me with a few hundred published
tables (the whole regression database), and things would degrade as
roughly O(published_relations * all_relations) beyond that.
Because the rules.out expected output changes, force a catversion bump.
Ordinarily we might not want to do that post-beta1; but we already know
we'll be doing a catversion bump before beta2 to fix pg_statistic_ext
issues, so it's pretty much free to fix it now instead of waiting for v13.
Per report and fix suggestion from PegoraroF10.
Discussion: https://postgr.es/m/1551385426763-0.post@n3.nabble.com
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