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Constraint Exclusion (Partitioning) - Initial Review requested

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: pgsql-patches(at)postgresql(dot)org
Subject: Constraint Exclusion (Partitioning) - Initial Review requested
Date: 2005-06-27 00:41:39
Message-ID: 1119832899.3690.37.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
I enclose a fully working implementation of Constraint Exclusion, a very
basic form of Partitioning. Initial review is requested, to allow us all
to assess what further work is required on this prior to Beta freeze.

Patch against current cvstip; passes make check and all special tests.

The main purpose of this feature is to reduce access time against large
tables that have been split into partitions by using the PostgreSQL
inheritance facility. It has been written in a very generic way allowing
a whole range of applications.

If
	a) a table is part of an inheritance set
	b) the table has check constraints defined upon it
	c) enable_constraint_exclusion = true

then the planner will attempt to use the definition of the Constraints
to see if that relation could ever have rows in it that the query might
see. *No* additional SQL DDL syntax is required to define this.

Only query clauses of the form ATTR OP CONSTANT will be considered, in a
very similar way to the way partial indexes work already.

The code changes effect only the planner, building upon the partial
index logic to allow refutation as well as implication.

There are clearly many questions to be answered by me and I'm happy to
do so, so please fire away. My hope is to get a more polished form of
this functionality into 8.1. Further developments on Partitioning are
foreseen, though the feature submitted today is the main building block
for any further work/optimization in this area and so additional
features will be discussed at a later time.

A full test suite has been specially written for this feature. This is
included here also, though no attempt has been made as yet to integrate
that with the main regression test suite (as yet). Required files are
included in a single tar file with this email. Extract these to the
PostgreSQL installation directory and run using ./testprange.sh
The test suite executes around 100 queries against 7 different database
designs, comparing results with/without the new enable option. Full and
pruned EXPLAINs are also derived during execution to allow easier
analysis of the success of the exclusion process (view the
testprange_t*e.out files).

There are no cases where any of the test queries returns a logically
incorrect answer; hence fully working. There are a few cases where
queries have not been optimised as far as possible; in those cases
checks on my propositional logic are requested... This is extremely
complex and my expectation is that testers/reviewers will find at least
of couple of logic improvements. The most frequent queries are believed
to work optimally.

There is no documentation at this time.

Main questions:
1. How should we handle the case where *all* inherited relations are
excluded? (This is not currently covered in the code).
2. Should this feature be available for all queries or just inherited
relations?
3. And should we extend RelOptInfo to include constraint information?
4. Do we want to integrate the test suite also?
5. Presumably a section under Performance tips would be appropriate to
document this feature? (As well as section in run-time parameters).

Additional thoughts:
1. We should be able to optimise the case where there is only a single
non-excluded relation by removing the Append node.

Best Regards, Simon Riggs

Attachment: testprange.tar
Description: application/x-tar (40.0 KB)
Attachment: partition1.patch
Description: text/x-patch (36.8 KB)

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