Date: Tue, 5 May 2020 12:50:01 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: PG 13 release notes, first draft
Message-ID: <20200505175001.GA28974@telsasoft.com>
References: <20200505031600.GB21752@momjian.us>
 <20200505164503.GY28974@telsasoft.com>
 <20200505171809.GF21185@momjian.us>
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On Tue, May 05, 2020 at 01:18:09PM -0400, Bruce Momjian wrote:
> > |Release date: 2020-05-03
> > => Should say 2020-XX-XX, before someone like me goes and installs it everywhere in sight.
> 
> Agreed!
> 
> > |These triggers cannot change the destination partition. 
> > => Maybe say "cannot change which partition is the destination"

Looks like you copied my quote mark :(

> > | Allow hash aggregation to use disk storage for large aggregation result sets (Jeff Davis) 
> > |  Previously, hash aggregation was not used if it was expected to use more than work_mem memory. This is controlled by enable_hashagg_disk. 
> > => enable_hashagg_disk doesn't behave like other enable_* parameters.
> > As I understand, disabling it only "opportunisitically" avoids plans which are
> > *expected* to overflow work_mem.  I think we should specifically say that, and
> > maybe suggest recalibrating work_mem.
> 
> I went with "avoided":
> 
> 	Previously, hash aggregation was avoided if it was expected to use more
> 	than work_mem memory.  This is controlled by enable_hashagg_disk.

I think we should expand on this:

|Previously, hash aggregation was avoided if it was expected to use more than
|work_mem memory, but it wasn't enforced, and hashing could still exceed
|work_mem.  To get back the old behavior, increasing work_mem.
|
|The parameter enable_hashagg_disk controls whether a plan which is *expected*
|to spill to disk will be considered.  During execution, an aggregate node which
|exceeding work_mem will spill to disk regardless of this parameter.

I wrote something similar here:
https://www.postgresql.org/message-id/20200407223900.GT2228%40telsasoft.com

> > | This is controlled by GUC wal_skip_threshold. 
> > I think you should say that's a size threshold which determines which strategy
> > to use (WAL or fsync).
> 
> I went with:
> 	The WAL write amount where this happens is controlled by wal_skip_threshold.
>
> They can use the doc link if they want more detail.

I guess I would say "relations larger than wal_skip_threshold will be fsynced
rather than copied to WAL"

-- 
Justin