Date: Sat, 7 Apr 2018 09:23:49 -0300
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Amit Langote <amitlangote09@gmail.com>
Cc: Andres Freund <andres@anarazel.de>,
	David Rowley <david.rowley@2ndquadrant.com>,
	Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>,
	Jesper Pedersen <jesper.pedersen@redhat.com>,
	Rajkumar Raghuwanshi <rajkumar.raghuwanshi@enterprisedb.com>,
	Beena Emerson <memissemerson@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>, amul sul <sulamul@gmail.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>,
	Dilip Kumar <dilipbalaut@gmail.com>
Subject: Re: [HACKERS] Runtime Partition Pruning
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Amit Langote wrote:

> See if the attached makes it any better.
> 
> Now I know we don't have the runtime pruning in yet, but since the
> proposed patch would extend its functionality I have included its
> description in the comment.

Thanks!

I edited it as attached, to 1. avoid mentioning functionality that
doesn't yet exist, and 2. avoid excessive internal detail (we want a
high-level overview here), which from experience gets outdated pretty
quickly.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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commit 28768290d8d9c58e76e2594a14d5b1f8465ba262=1B[m
Author:     Alvaro Herrera <alvherre@alvh.no-ip.org>
AuthorDate: Sat Apr 7 08:44:12 2018 -0300
CommitDate: Sat Apr 7 09:20:58 2018 -0300

    Add some documentation to partprune.c
   =20
    Author: Amit Langote
    Discussion: https://postgr.es/m/CA+HiwqGzq4D6z=3D8R0AP+XhbTFCQ-4Ct+t2ek=
qjE9Fpm84_JUGg@mail.gmail.com

diff --git a/src/backend/partitioning/partprune.c b/src/backend/partitionin=
g/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 containe=
d in
+ * table's partition descriptor and query clauses.
+ *
+ * During planning, clauses that can be matched to the table's partition k=
ey
+ * are turned into a set of "pruning steps", which are then executed to
+ * produce a set of RTIs of partitions whose bounds satisfy the constraint=
s 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 cont=
ains
+ * information extracted from one or more clauses that are matched to the
+ * (possibly multi-column) partition key, such as the expressions whose va=
lues
+ * to match against partition bounds and operator strategy to associate to
+ * each expression.  The other kind is a "combine" pruning step, which com=
bines
+ * the outputs of some other steps using the appropriate combination metho=
d.
+ * 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

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