Re: poor performance when recreating constraints on large tables
От
Samuel Gendler
Тема
Re: poor performance when recreating constraints on large tables
Дата
Msg-id
BANLkTim5GO2k0m7E2=KevdZrMPwH-9aCDg@mail.gmail.com
Ответ на
Re: poor performance when recreating constraints on
large tables (Kevin Grittner)
Список
Дерево обсуждения
poor performance when recreating constraints on large tables Mike Broers <mbroers@gmail.com>
Re: poor performance when recreating constraints on large tables Tom Lane <tgl@sss.pgh.pa.us>
Re: poor performance when recreating constraints on large tables Mike Broers <mbroers@gmail.com>
Re: poor performance when recreating constraints on large tables Robert Haas <robertmhaas@gmail.com>
Re: poor performance when recreating constraints on large tables Samuel Gendler <sgendler@ideasculptor.com>
Re: poor performance when recreating constraints on
large tables "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
Re: poor performance when recreating constraints on large tables Samuel Gendler <sgendler@ideasculptor.com>
Re: poor performance when recreating constraints on large
tables Greg Smith <greg@2ndquadrant.com>
Re: poor performance when recreating constraints on large tables Samuel Gendler <sgendler@ideasculptor.com>
On Wed, Jun 8, 2011 at 12:53 PM, Kevin Grittner <Kevin.Grittner@wicourts.gov> wrote:
Samuel Gendler <sgendler@ideasculptor.com> wrote:And it is sometimes off by orders of magnitude. How much remaining
> The planner knows how many rows are expected for each step of the
> query plan, so it would be theoretically possible to compute how
> far along it is in processing a query based on those estimates,
> wouldn't it?
time do you report when the number of rows actually processed so far
is five times the estimated rows that the step would process? How
about after it chugs on from there to 20 time she estimated row
count? Of course, on your next query it might finish after
processing only 5% of the estimated rows....
Sure, but if it is a query that is slow enough for a time estimate to be useful, odds are good that stats that are that far out of whack would actually be interesting to whoever is looking at the time estimate, so showing some kind of 'N/A' response once things have gotten out of whack wouldn't be unwarranted. Not that I'm suggesting that any of this is a particularly useful exercise. I'm just playing with the original thought experiment suggestion.
-Kevin
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