Constraint Exclusion (Partitioning) - Initial Review requested - Mailing list pgsql-patches
From | Simon Riggs |
---|---|
Subject | Constraint Exclusion (Partitioning) - Initial Review requested |
Date | |
Msg-id | 1119832899.3690.37.camel@localhost.localdomain Whole thread Raw |
Responses |
Re: Constraint Exclusion (Partitioning) - Initial Review
Re: Constraint Exclusion (Partitioning) - Initial Review requested Re: Constraint Exclusion (Partitioning) - Initial Review |
List | pgsql-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
pgsql-patches by date: