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Here we add ExprState support for obtaining a 32-bit hash value from a list of expressions. This allows both faster hashing and also JIT compilation of these expressions. This is especially useful when hash joins have multiple join keys as the previous code called ExecEvalExpr on each hash join key individually and that was inefficient as tuple deformation would have only taken into account one key at a time, which could lead to walking the tuple once for each join key. With the new code, we'll determine the maximum attribute required and deform the tuple to that point only once. Some performance tests done with this change have shown up to a 20% performance increase of a query containing a Hash Join without JIT compilation and up to a 26% performance increase when JIT is enabled and optimization and inlining were performed by the JIT compiler. The performance increase with 1 join column was less with a 14% increase with and without JIT. This test was done using a fairly small hash table and a large number of hash probes. The increase will likely be less with large tables, especially ones larger than L3 cache as memory pressure is more likely to be the limiting factor there. This commit only addresses Hash Joins, but lays expression evaluation and JIT compilation infrastructure for other hashing needs such as Hash Aggregate. Author: David Rowley Reviewed-by: Alexey Dvoichenkov <alexey@hyperplane.net> Reviewed-by: Tels <nospam-pg-abuse@bloodgate.com> Discussion: https://postgr.es/m/CAApHDvoexAxgQFNQD_GRkr2O_eJUD1-wUGm%3Dm0L%2BGc%3DT%3DkEa4g%40mail.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/.