From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
Cc: | "Tomas Vondra" <tv(at)fuzzy(dot)cz>, "Robert Haas" <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: estimating # of distinct values |
Date: | 2010-12-27 22:55:12 |
Message-ID: | 7214.1293490512@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> With respect to (b), I think I'd need to see a much more detailed
>> design for how you intend to make this work. Off the top of my
>> head there seems to be some pretty serious feasibility problems.
> I had one random thought on that -- it seemed like a large concern
> was that there would need to be at least an occasional scan of the
> entire table to rebuild the distinct value information. Don't we
> already require an occasional scan of the entire table for freezing
> transaction IDs? Could this be part of any vacuum of the entire
> table?
Well, first, those scans occur only once every few hundred million
transactions, which is not likely a suitable timescale for maintaining
statistics. And second, we keep on having discussions about rejiggering
the whole tuple-freezing strategy. Even if piggybacking on those scans
looked useful, it'd be unwise to assume it'll continue to work the same
way it does now.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Kevin Grittner | 2010-12-27 23:04:20 | Re: estimating # of distinct values |
Previous Message | Kevin Grittner | 2010-12-27 22:49:51 | Re: estimating # of distinct values |