Re: Big performance slowdown from 11.2 to 13.3

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Subject: Re: Big performance slowdown from 11.2 to 13.3
From: "David G. Johnston" <david.g.johnston@xxxxxxxxx>
Date: Tue, 27 Jul 2021 20:06:59 -0700
Cc: Tom Lane <tgl@xxxxxxxxxxxxx>, Peter Geoghegan <pg@xxxxxxx>, David Rowley <dgrowleyml@xxxxxxxxx>, Justin Pryzby <pryzby@xxxxxxxxxxxxx>, "pgsql-performance@xxxxxxxxxxxxxx" <pgsql-performance@xxxxxxxxxxxxxx>
In-reply-to: <MN2PR15MB2560987D103C712238C706AB85EA9@MN2PR15MB2560.namprd15.prod.outlook.com>
References: <MN2PR15MB25601E80A9B6D1BA6F592B1985E39@MN2PR15MB2560.namprd15.prod.outlook.com> <20210721191528.GC19620@telsasoft.com> <MN2PR15MB256016E33F00DE60B96F02D385E39@MN2PR15MB2560.namprd15.prod.outlook.com> <CAH2-Wzm3rSAWHyENb3T0X8M_qdYjF1t7rntkMJ2kDiuhVOHx3g@mail.gmail.com> <MN2PR15MB2560C1A890DC07F9359FB56285E39@MN2PR15MB2560.namprd15.prod.outlook.com> <732758.1626911007@sss.pgh.pa.us> <MN2PR15MB2560778595BB7AF6E691B26785E39@MN2PR15MB2560.namprd15.prod.outlook.com> <MN2PR15MB2560D429866BD65A70574A6C85E49@MN2PR15MB2560.namprd15.prod.outlook.com> <CAApHDvqoF7y7SQjGT=940njnAd_CUcUG6oRYChcP_+eJyuNiug@mail.gmail.com> <MN2PR15MB25603D3CE06C8F9C312EA58985E49@MN2PR15MB2560.namprd15.prod.outlook.com> <MN2PR15MB2560E4574A6E2B5AED2C03CB85E49@MN2PR15MB2560.namprd15.prod.outlook.com> <784576.1626968702@sss.pgh.pa.us> <785218.1626969409@sss.pgh.pa.us> <CAApHDvo+Gb80BVPKYCwHbLa7a7ZXp9ziq9URrpQaKdvXsd46bg@mail.gmail.com> <786600.1626970898@sss.pgh.pa.us> <787780.1626972122@sss.pgh.pa.us> <MN2PR15MB25609F3505A6FB441CAB22A585E49@MN2PR15MB2560.namprd15.prod.outlook.com> <171155.1627236507@sss.pgh.pa.us> <MN2PR15MB2560987D103C712238C706AB85EA9@MN2PR15MB2560.namprd15.prod.outlook.com>

On Tue, Jul 27, 2021 at 7:57 PM ldh@xxxxxxxxxxxxxxxxxx <ldh@xxxxxxxxxxxxxxxxxx> wrote:

hash_mem_multiplier is an upper-bound right: it doesn't reserve memory ahead of time correct?

Yes, that is what the phrasing "maximum amount" in the docs is trying to convey.

https://www.postgresql.org/docs/current/runtime-config-resource.html#RUNTIME-CONFIG-RESOURCE-MEMORY

But also note that it is "each operation" that gets access to that limit.

David J.

References:
- Big performance slowdown from 11.2 to 13.3
  - From: ldh@xxxxxxxxxxxxxxxxxx
- Re: Big performance slowdown from 11.2 to 13.3
  - From: Justin Pryzby
- RE: Big performance slowdown from 11.2 to 13.3
  - From: ldh@xxxxxxxxxxxxxxxxxx
- Re: Big performance slowdown from 11.2 to 13.3
  - From: Peter Geoghegan
- RE: Big performance slowdown from 11.2 to 13.3
  - From: ldh@xxxxxxxxxxxxxxxxxx
- Re: Big performance slowdown from 11.2 to 13.3
  - From: Tom Lane
- RE: Big performance slowdown from 11.2 to 13.3
  - From: ldh@xxxxxxxxxxxxxxxxxx
- RE: Big performance slowdown from 11.2 to 13.3
  - From: ldh@xxxxxxxxxxxxxxxxxx
- Re: Big performance slowdown from 11.2 to 13.3
  - From: David Rowley
- RE: Big performance slowdown from 11.2 to 13.3
  - From: ldh@xxxxxxxxxxxxxxxxxx
- RE: Big performance slowdown from 11.2 to 13.3
  - From: ldh@xxxxxxxxxxxxxxxxxx
- Re: Big performance slowdown from 11.2 to 13.3
  - From: Tom Lane
- Re: Big performance slowdown from 11.2 to 13.3
  - From: Tom Lane
- Re: Big performance slowdown from 11.2 to 13.3
  - From: David Rowley
- Re: Big performance slowdown from 11.2 to 13.3
  - From: Tom Lane
- Re: Big performance slowdown from 11.2 to 13.3
  - From: Tom Lane
- RE: Big performance slowdown from 11.2 to 13.3
  - From: ldh@xxxxxxxxxxxxxxxxxx
- Re: Big performance slowdown from 11.2 to 13.3
  - From: Tom Lane
- RE: Big performance slowdown from 11.2 to 13.3
  - From: ldh@xxxxxxxxxxxxxxxxxx

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