d80b022501
In commit bd3e3e9e5, I over-hastily used 1 / rel->rows as the assumed frequency of entries in a column that ANALYZE has found to be unique. However, rel->rows is the number of table rows that are estimated to pass the query's restriction conditions, so that we got a too-large result if the query has selective restrictions. What I should have used is 1 / rel->tuples, since that is the estimated total number of table rows. The pre-existing code path that digs a frequency out of the histogram produces a frequency relative to the whole table, so surely this new alternative code path must do so as well. Any correction needed on the basis of selectivity must be done by the user of the mcv_freq value. Fixing this causes all the regression test plans changed by bd3e3e9e5 to revert to what they had been, except for the first change in join.out. As I correctly argued in bd3e3e9e5, in that test case we have no stats and should not risk a hash join. Evidently I was less correct to argue that the other changes were improvements. Reported-by: Joel Jacobson <joel@compiler.org> Diagnosed-by: Tender Wang <tndrwang@gmail.com> Author: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/341b723c-da45-4058-9446-1514dedb17c1@app.fastmail.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.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.