Subject: Re: multivariate statistics v14
To: Tatsuo Ishii <ishii@postgresql.org>
References: <1457544102.24545.79.camel@2ndquadrant.com>
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 <20160316.115824.1975980662850012690.t-ishii@sraoss.co.jp>
Cc: jeff.janes@gmail.com, alvherre@2ndquadrant.com,
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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <743161cc-771d-6e2b-c43f-4f2bd1fe6d42@2ndquadrant.com>
Date: Wed, 16 Mar 2016 14:45:46 +0100
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Hi,

On 03/16/2016 03:58 AM, Tatsuo Ishii wrote:
> I apology if it's already discussed. I am new to this patch.
>
>> Attached is v15 of the patch series, fixing this and also doing quite a
>> few additional improvements:
>>
>> * added some basic examples into the SGML documentation
>>
>> * addressing the objectaddress omissions, as pointed out by Alvaro
>>
>> * support for ALTER STATISTICS ... OWNER TO / RENAME / SET SCHEMA
>>
>> * significant refactoring of MCV and histogram code, particularly
>>   serialization, deserialization and building
>>
>> * reworking the functional dependencies to support more complex
>>   dependencies, with multiple columns as 'conditions'
>>
>> * the reduction using functional dependencies is also significantly
>>   simplified (I decided to get rid of computing the transitive closure
>>   for now - it got too complex after the multi-condition dependencies,
>>   so I'll leave that for the future
>
> Do you have any other missing parts in this work? I am asking
> because I wonder if you want to push this into 9.6 or rather 9.7.

I think the first few parts of the patch series, namely:

   * shared infrastructure (0002)
   * functional dependencies (0003)
   * MCV lists (0004)
   * histograms (0005)

might make it into 9.6. I believe the code for building and storing the 
different kinds of stats is reasonably solid. What probably needs more 
thorough review are the changes in clauselist_selectivity(), but the 
code in these parts is reasonably simple as it only supports using a 
single multi-variate statistics per relation.

The part (0006) that allows using multiple statistics (i.e. selects 
which of the available stats to use and in what order) is probably the 
most complex part of the whole patch, and I myself do have some 
questions about some aspects of it. I don't think this part might get 
into 9.6 at this point (although it'd be nice if we managed to do that).

I can also imagine moving the ndistinct pieces forward, in front of 0006 
if that helps getting it into 9.6. There's a bit more work on making it 
more flexible, though, to allow handling subsets columns (currently we 
need a perfect match).


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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