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From: Josh Berkus <josh@agliodbs.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: PATCH: adaptive ndistinct estimator v4
Date: Fri, 15 May 2015 13:00:19 -0700
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On 05/15/2015 12:58 PM, Robert Haas wrote:
> On Fri, May 15, 2015 at 3:35 PM, Josh Berkus <josh@agliodbs.com> wrote:
>> On 05/15/2015 11:30 AM, Robert Haas wrote:
>>> Once we enter beta (or even feature freeze), it's too late to whack
>>> around the algorithm heavily.  We're pretty much committed to
>>> releasing and supporting whatever we have got at that point.  I guess
>>> we could revert it if it doesn't work out, but that's about the only
>>> option at that point.  We have more flexibility during the main part
>>> of the development cycle.  But your point is certainly valid and I
>>> don't mean to dispute it.
>>
>> I will finally have a customer workload available to test this on this
>> weekend.  That's been rather delayed by the availability of customer
>> hardware,because I'm not allowed to copy out the database.  However,
>> this is a database which suffers from multiple ndistinct estimation
>> issues in production, so I should be able to get a set of stats back by
>> Monday which would show how much of a general improvement it is.
>>
>> I realize that's after the deadline, but there wasn't much I could do
>> about it.  I've tried to simulate the kind of estimation issues I've
>> seen, but they don't simulate well.
> 
> This is clearly 9.6 material at this point, and has been for a while.
> The patch - at least the last version I looked at - didn't store
> anything different in pg_statistic.  It just logged what it would have
> stored.  So testing is good, but there's not a question of pushing
> this into 9.5.

I'm personally OK with that.  The last thing we want to do is make query
costing changes *in haste*.

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com


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