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The following are the individual improvements: 1) Avoidance of FunctionCallInfo based function calls, replaced by more efficient functions with a native C argument interface. 2) Don't extract columns from a cache entry's tuple whenever matching entries - instead store them as a Datum array. This also allows to get rid of having to build dummy tuples for negative & list entries, and of a hack for dealing with cstring vs. text weirdness. 3) Reorder members of catcache.h struct, so imortant entries are more likely to be on one cacheline. 4) Allowing the compiler to specialize critical SearchCatCache for a specific number of attributes allows to unroll loops and avoid other nkeys dependant initialization. 5) Only initializing the ScanKey when necessary, i.e. catcache misses, greatly reduces cache unnecessary cpu cache misses. 6) Split of the cache-miss case from the hash lookup, reducing stack allocations etc in the common case. 7) CatCTup and their corresponding heaptuple are allocated in one piece. This results in making cache lookups themselves roughly three times as fast - full-system benchmarks obviously improve less than that. I've also evaluated further techniques: - replace open coded hash with simplehash - the list walk right now shows up in profiles. Unfortunately it's not easy to do so safely as an entry's memory location can change at various times, which doesn't work well with the refcounting and cache invalidation. - Cacheline-aligning CatCTup entries - helps some with performance, but the win isn't big and the code for it is ugly, because the tuples have to be freed as well. - add more proper functions, rather than macros for SearchSysCacheCopyN etc., but right now they don't show up in profiles. The reason the macro wrapper for syscache.c/h have to be changed, rather than just catcache, is that doing otherwise would require exposing the SysCache array to the outside. That might be a good idea anyway, but it's for another day. Author: Andres Freund Reviewed-By: Robert Haas Discussion: https://postgr.es/m/20170914061207.zxotvyopetm7lrrp@alap3.anarazel.de |
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README
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/.