| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Gregory Stark <stark(at)enterprisedb(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, "jd(at)commandprompt(dot)com" <jd(at)commandprompt(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Greg Smith <gsmith(at)gregsmith(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: benchmarking the query planner |
| Date: | 2008-12-11 23:43:48 |
| Message-ID: | 13761.1229039028@sss.pgh.pa.us |
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Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> On Thu, 2008-12-11 at 17:45 -0500, Tom Lane wrote:
>> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
>>> I would like it even more if there was a data type specific default.
>>> Currently we have a special case for boolean, but that's it.
>>
>> No, we don't (or if we do I'd be interested to know where).
> Your commit, selfuncs.c, 7 Jul.
As with Robert's pointer, that's about coping with missing stats,
not about determining what stats to collect.
> ... neither of those were ones I was thinking about. I see 3 main classes:
> * data with small number of distinct values (e.g. boolean, smallint)
> * data with many distinct values
> * data with where every value is typically unique (e.g. text)
These three categories are already dealt with in an entirely
type-independent fashion by the heuristics in compute_scalar_stats.
I think it's quite appropriate to drive them off the number of observed
values, not guesses about what a particular datatype is used for.
regards, tom lane
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