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Previously aggregate transition and combination functions were invoked by special case code in nodeAgg.c, evaluating input and filters separately using the expression evaluation machinery. That turns out to not be great for performance for several reasons: - repeated expression evaluations have some cost - the transition functions invocations are poorly predicted, as commonly there are multiple aggregates in a query, resulting in the same call-stack invoking different functions. - filter and input computation had to be done separately - the special case code made it hard to implement JITing of the whole transition function invocation Address this by building one large expression that computes input, evaluates filters, and invokes transition functions. This leads to moderate speedups in queries bottlenecked by aggregate computations, and enables large speedups for similar cases once JITing is done. There's potential for further improvement: - It'd be nice if we could simplify the somewhat expensive aggstate->all_pergroups lookups. - right now there's still an advance_transition_function invocation in nodeAgg.c, leading to some code duplication. Author: Andres Freund Discussion: https://postgr.es/m/20170901064131.tazjxwus3k2w3ybh@alap3.anarazel.de |
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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. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.