commit 28768290d8d9c58e76e2594a14d5b1f8465ba262 Author: Alvaro Herrera AuthorDate: Sat Apr 7 08:44:12 2018 -0300 CommitDate: Sat Apr 7 09:20:58 2018 -0300 Add some documentation to partprune.c Author: Amit Langote Discussion: https://postgr.es/m/CA+HiwqGzq4D6z=8R0AP+XhbTFCQ-4Ct+t2ekqjE9Fpm84_JUGg@mail.gmail.com diff --git a/src/backend/partitioning/partprune.c b/src/backend/partitioning/partprune.c index 959ee1643d..07b8057e3f 100644 --- a/src/backend/partitioning/partprune.c +++ b/src/backend/partitioning/partprune.c @@ -1,10 +1,27 @@ /*------------------------------------------------------------------------- * * partprune.c - * Parses clauses attempting to match them up to partition keys of a - * given relation and generates a set of "pruning steps", which can be - * later "executed" either from the planner or the executor to determine - * the minimum set of partitions which match the given clauses. + * Support for partition pruning during query planning + * + * This module implements partition pruning using the information contained in + * table's partition descriptor and query clauses. + * + * During planning, clauses that can be matched to the table's partition key + * are turned into a set of "pruning steps", which are then executed to + * produce a set of RTIs of partitions whose bounds satisfy the constraints in + * the step. Partitions not in the set are said to have been pruned. + * + * There are two kinds of pruning steps: a "base" pruning step, which contains + * information extracted from one or more clauses that are matched to the + * (possibly multi-column) partition key, such as the expressions whose values + * to match against partition bounds and operator strategy to associate to + * each expression. The other kind is a "combine" pruning step, which combines + * the outputs of some other steps using the appropriate combination method. + * All steps that are constructed are executed in succession such that for any + * "combine" step, all of the steps whose output it depends on are executed + * first and their ouput preserved. + * + * See gen_partprune_steps_internal() for more details on step generation. * * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California