mirror of
https://github.com/postgres/postgres.git
synced 2025-05-06 19:59:18 +03:00
5874c70557
This test script verifies that KNN searches of an SP-GiST index produce the same sort order as a seqscan-and-sort. The FULL JOINs used for that are exceedingly slow, however. Investigation shows that the problem is that the initial join is on the rank() values, and we have a lot of duplicates due to the data set containing 1000 duplicate points. We're therefore going to produce 1000000 join rows that have to be thrown away again by the join filter. We can improve matters by using row_number() instead of rank(), so that the initial join keys are unique. The catch is that that makes the results sensitive to the sorting of rows with equal distances from the reference point. That doesn't matter for the actually-equal points, but as luck would have it, the data set also contains two distinct points that have identical distances to the origin. So those two rows could legitimately appear in either order, causing unwanted output from the check queries. However, it doesn't seem like it's the job of this test to check whether the <-> operator correctly computes distances; its charter is just to verify that SP-GiST emits the values in distance order. So we can dodge the indeterminacy problem by having the check only compare row numbers and distances not the actual point values. This change reduces the run time of create_index_spgist by a good three-quarters, on my machine, with ensuing beneficial effects on the runtime of create_index (thanks to interactions with CREATE INDEX CONCURRENTLY tests in the latter). I see a net improvement of more than 2X in the runtime of their parallel test group. Discussion: https://postgr.es/m/735.1554935715@sss.pgh.pa.us
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/.