9f404d7922
To estimate with extended statistics, we need to clear the varnullingrels
field in the expression, and duplicates are not allowed in the GroupVarInfo
list. We might re-use add_unique_group_var(), but we don't do so for two
reasons.
1) We must keep the origin_rinfos list ordered exactly the same way as
varinfos.
2) add_unique_group_var() is designed for estimate_num_groups(), where a
larger number of groups is worse. While estimating the number of hash
buckets, we have the opposite: a lesser number of groups is worse.
Therefore, we don't have to remove "known equal" vars: the removed var
may valuably contribute to the multivariate statistics to grow the number
of groups.
This commit adds custom code to estimate_multivariate_bucketsize() to
initialize varinfos properly.
Reported-by: Robins Tharakan <tharakan@gmail.com>
Discussion: https://postgr.es/m/18885-da51324078588253%40postgresql.org
Author: Andrei Lepikhov <lepihov@gmail.com>
Reviewed-by: David Rowley <dgrowleyml@gmail.com>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
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