e6a1d8f5ac
The previous idea was "scale up the bucketsize estimate by the ratio
of the MCV's frequency to the average value's frequency". But we
should have been suspicious of that plan, since it frequently led to
impossible (> 1) values which we had to apply an ad-hoc clamp to.
Joel Jacobson demonstrated that it sometimes leads to making the
wrong choice about which side of the hash join should be inner.
Instead, drop the whole business of estimating average frequency, and
just clamp the bucketsize estimate to be at least the MCV's frequency.
This corresponds to the bucket size we'd get if only the MCV appears
in a bucket, and the MCV's frequency is not affected by the
WHERE-clause filters. (We were already making the latter assumption.)
This also matches the coding used since
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| configure | ||
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| COPYRIGHT | ||
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| HISTORY | ||
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| README.md | ||
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/.