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Up to now, all of the "catcache list" objects within a catalog cache were just chained together on a single dlist, requiring O(N) time to search. Remarkably, we've not had serious performance problems with that so far; but we got a complaint of a bad performance regression from v15 in a case with a large number of roles in the system, which traced down to O(N^2) total time when we probed N catcache lists. Replace that data structure with a hashtable having an enlargeable number of dlists, in an exactly parallel way to the data structure we've used for years for the plain CatCTup cache members. The extra cost of maintaining a hash table seems negligible, since we were already computing a hash value for list searches. Normally this'd be HEAD-only material, but in view of the performance regression it seems advisable to back-patch into v16. In the v16 version of the patch, leave the dead cc_lists field where it is and add the new fields at the end of struct catcache, to avoid possible ABI breakage in case any external code is looking at these structs. (We assume no external code is actually allocating new catcache structs.) Per report from alex work. Discussion: https://postgr.es/m/CAGvXd3OSMbJQwOSc-Tq-Ro1CAz=vggErdSG7pv2s6vmmTOLJSg@mail.gmail.com |
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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/.