Fix costing bug in MergeAppend When building a MergeAppendPath which has child paths that are not sorted correctly for the MergeAppend's sort order, we apply the cost of sorting those paths to the MergeAppendPath costs.
Here we fix a bug where the number of tuples specified that needed to be sorted was effectively pg_class.reltuples rather than the number of expected row in the subpath. This effectively penalizes MergeAppend plans any time any filter is present on the MergeAppend subpath as the sort cost added is to sort all tuples in the table rather than just the ones expected the path to return. This did not affect UNION ALL type queries as the RelOptInfo tuples is set from the subquery's path rows. It does affect MergeAppends uses for inheritance and partitioned tables. This is a long-standing bug introduced when MergeAppend was first added in 11cad29c9. No backpatch as this could result in plan changes. Author: Alexander Kuzmenkov Reviewed-by: Ashutosh Bapat, Aleksander Alekseev, David Rowley Discussion: https://postgr.es/m/CALzhyqyhoXQDR-Usd_0HeWk%3DuqNLzoVeT8KhRoo%3DpV_KzgO3QQ%40mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/9d1a5354f58cf61d9be6733d5ad0b36936af5af3 Modified Files -------------- src/backend/optimizer/util/pathnode.c | 2 +- src/test/regress/expected/inherit.out | 23 +++++++++++++++++++++++ src/test/regress/sql/inherit.sql | 13 +++++++++++++ 3 files changed, 37 insertions(+), 1 deletion(-)
