| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Jan Wieck <jan(at)wi3ck(dot)info>, Gregory Smith <gregsmithpgsql(at)gmail(dot)com>, John Naylor <john(dot)naylor(at)enterprisedb(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Subject: | Re: The Free Space Map: Problems and Opportunities |
| Date: | 2021-08-18 19:58:27 |
| Message-ID: | CAH2-WzmaEQnFYy7_TWoPfGOghVX63xUuq6GF_=Ovm7C47UyLNQ@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
On Tue, Aug 17, 2021 at 5:31 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> > Now what's the threshold? 20 out of 100? 50? 80?
>
> I'm not going to pretend to know the answer. But I will point out that
> one DB system whose heap fill factor defaults to 90 seems to have a
> symmetric setting for the "open up page again" point -- the default
> for that is 40. Not sure that that really matters to us, but that does
> seem pretty low to me. It's very sticky indeed.
Correction: it's actually 60, not 40.
It's true that the actual default is 40, but it works the other way
around relative to Postgres (as does the related fill factor like
setting, which defaults to 90 instead of 100). And so we would think
of this other "open up closed page once again" setting as having a
default of 60. (Or perhaps we'd think of it as having a default that
is 2/3 of the closely related fill factor setting's default.)
--
Peter Geoghegan
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Bossart, Nathan | 2021-08-18 20:35:12 | Re: .ready and .done files considered harmful |
| Previous Message | Justin Pryzby | 2021-08-18 19:23:18 | Re: strange case of "if ((a & b))" |