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If we have DECHIST statistics about the argument expression, use the average number of distinct elements as the array length estimate. (It'd be better to use the average total number of elements, but that is not currently calculated by compute_array_stats(), and it's unclear that it'd be worth extra effort to get.) To do this, we have to change the signature of estimate_array_length to pass the "root" pointer. While at it, also change its result type to "double". That's probably not really necessary, but it avoids any risk of overflow of the value extracted from DECHIST. All existing callers are going to use the result in a "double" calculation anyway. Paul Jungwirth, reviewed by Jian He and myself Discussion: https://postgr.es/m/CA+renyUnM2d+SmrxKpDuAdpiq6FOM=FByvi6aS6yi__qyf6j9A@mail.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 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/.