| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
| Cc: | Serge Rielau <serge(at)rielau(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Rushabh Lathia <rushabh(dot)lathia(at)gmail(dot)com>, Prabhat Sahu <prabhat(dot)sahu(at)enterprisedb(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Rafia Sabih <rafia(dot)sabih(at)enterprisedb(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Oleg Golovanov <rentech(at)mail(dot)ru> |
| Subject: | Re: Treating work_mem as a shared resource (Was: Parallel Hash take II) |
| Date: | 2017-11-17 23:23:40 |
| Message-ID: | CA+TgmoZtMAXVz+X5OEvX-J00AEwQT5TTKTeD98J2+je0ELG2Fg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Nov 17, 2017 at 1:22 PM, Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> Right. The ability for sorts to do well with less memory is really
> striking these days. And though I didn't mean to seriously suggest it,
> a hash_mem GUC does seem like it solves some significant problems
> without much risk. I think it should be hash_mem, not sort_mem,
> because hashing seems more like the special case among operations that
> consume work_mem, and because sort_mem is already the old name for
> work_mem that is still accepted as a work_mem alias, and because
> hash_mem avoids any confusion about whether or not CREATE INDEX uses
> the new GUC (it clearly does not).
Hmm. I wonder if you are correct that hashing is the special case.
Hashing and sorting are of course the two main operations -- but
there's materialize and anything else that uses a CTE, and maybe other
stuff I'm not thinking about right now. You might be right that hash
is the one where it really matters, but it's probably worth a bit more
reflection on where it matters most and for what reasons.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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