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Alexander Korotkov 6bb6a62f3c Use extended stats for precise estimation of bucket size in hash join ... Recognizing the real-life complexity where columns in the table often have functional dependencies, PostgreSQL's estimation of the number of distinct values over a set of columns can be underestimated (or much rarely, overestimated) when dealing with multi-clause JOIN. In the case of hash join, it can end up with a small number of predicted hash buckets and, as a result, picking non-optimal merge join. To improve the situation, we introduce one additional stage of bucket size estimation - having two or more join clauses estimator lookup for extended statistics and use it for multicolumn estimation. Clauses are grouped into lists, each containing expressions referencing the same relation. The result of the multicolumn estimation made over such a list is combined with others according to the caller's logic. Clauses that are not estimated are returned to the caller for further estimation. Discussion: https://postgr.es/m/52257607-57f6-850d-399a-ec33a654457b%40postgrespro.ru Author: Andrei Lepikhov <lepihov@gmail.com> Reviewed-by: Andy Fan <zhihui.fan1213@gmail.com> Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com> Reviewed-by: Alena Rybakina <lena.ribackina@yandex.ru> Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>		10 months ago
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access	Make parallel nbtree index scans use an LWLock.	10 months ago
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commands	Remove support for temporal RESTRICT foreign keys	10 months ago
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optimizer	Use extended stats for precise estimation of bucket size in hash join	10 months ago
parser	Don't try to parallelize array_agg() on an anonymous record type.	10 months ago
partitioning	Fix bug in cbc127917 to handle nested Append correctly	11 months ago
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postmaster	Split WaitEventSet functions to separate source file	10 months ago
regex	Support PG_UNICODE_FAST locale in the builtin collation provider.	12 months ago
replication	Fix incorrect assertion in libpqwalreceiver	10 months ago
rewrite	Eliminate code duplication in replace_rte_variables callbacks	11 months ago
snowball	Update to latest Snowball sources.	11 months ago
statistics	Address stats import review comments.	10 months ago
storage	Make parallel nbtree index scans use an LWLock.	10 months ago
tcop	Rename some signal and interrupt handling functions for consistency	10 months ago
tsearch	Clear errno before calling strtol() in spell.c.	10 months ago
utils	Use extended stats for precise estimation of bucket size in hash join	10 months ago
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