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Document partprune.c a little better 

Author: Amit Langote
Reviewed-by: Álvaro Herrera, David Rowley
Discussion: https://postgr.es/m/CA+HiwqGzq4D6z=8R0AP+XhbTFCQ-4Ct+t2ekqjE9Fpm84_JUGg@mail.gmail.com
This commit is contained in:
Alvaro Herrera 2018-04-07 10:35:38 -03:00
parent 4f813c7203
commit 971d7ddbe1
1 changed files with 24 additions and 5 deletions
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29
src/backend/partitioning/partprune.c
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@ -1,10 +1,28 @@
/*-------------------------------------------------------------------------
*
* 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 partitions (as indexes of the RelOptInfo->part_rels array)
* that 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
@ -256,7 +274,8 @@ prune_append_rel_partitions(RelOptInfo *rel)
* get_matching_partitions
* Determine partitions that survive partition pruning
*
* Returns a Bitmapset of indexes of surviving partitions.
* Returns a Bitmapset of the RelOptInfo->part_rels indexes of the surviving
* partitions.
*/
Bitmapset *
get_matching_partitions(PartitionPruneContext *context, List *pruning_steps)