Fix O(N^2) performance issue in pg_publication_tables view

Enterprise / PostgreSQL - Tom Lane [sss.pgh.pa.us] - 22 May 2019 15:47 EDT

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

166f69f769 Fix O(N^2) performance issue in pg_publication_tables view.
src/backend/catalog/system_views.sql | 7 ++++---
src/include/catalog/catversion.h | 2 +-
src/test/regress/expected/rules.out | 4 ++--
3 files changed, 7 insertions(+), 6 deletions(-)

Upstream: git.postgresql.org


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