Subject: Re: Auxiliary Processes and MyAuxProc
To: Mike Palmiotto <mike.palmiotto@crunchydata.com>,
 Justin Pryzby <pryzby@telsasoft.com>
References: <20200317215218.GC26184@telsasoft.com>
 <20200318010433.GA17520@alvherre.pgsql>
 <CAMN686GixjieQhS9DtRvvAX9q73Px25yWuyWZRWeHh81ZE4XvA@mail.gmail.com>
 <20200318141720.GH26184@telsasoft.com>
 <CAMN686EB6MJDC2eMy1TES_Mz=UYree6GRFy-U5ob+ONtKDa_GQ@mail.gmail.com>
 <CAMN686GXRr2nZECF-zP5jz_uC6kxS7wnmNfQMjgf4hQLX6m7fA@mail.gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
 Michael Paquier <michael@paquier.xyz>, Andres Freund <andres@anarazel.de>,
 Yuli Khodorkovskiy <yuli.khodorkovskiy@crunchydata.com>,
 Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers <pgsql-hackers@postgresql.org>
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Organization: 2ndQuadrant
Message-ID: <bc2a012a-c652-33a9-1fd7-5eaa0944ec2e@2ndquadrant.com>
Date: Thu, 19 Mar 2020 11:35:41 +0100
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:52.0)
 Gecko/20100101 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: 
 <CAMN686GXRr2nZECF-zP5jz_uC6kxS7wnmNfQMjgf4hQLX6m7fA@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2020-03-18 17:07, Mike Palmiotto wrote:
> On Wed, Mar 18, 2020 at 11:26 AM Mike Palmiotto
> <mike.palmiotto@crunchydata.com> wrote:
>>
>> On Wed, Mar 18, 2020 at 10:17 AM Justin Pryzby <pryzby@telsasoft.com> wrote:
>>> Also, I saw this was failing tests both before and after my rebase.
>>>
>>> http://cfbot.cputube.org/
>>> https://ci.appveyor.com/project/postgresql-cfbot/postgresql/builds/31535161
>>> https://ci.appveyor.com/project/postgresql-cfbot/postgresql/builds/31386446
>>
>> Good catch, thanks. Will address this as well in the next round. Just
>> need to set up a Windows dev environment to see if I can
>> reproduce/fix.
> 
> While I track this down, here is a rebased patchset, which drops
> MySubprocessType and makes use of the MyBackendType.

While working on (My)BackendType, I was attempting to get rid of 
(My)AuxProcType altogether.  This would mostly work except that it's 
sort of wired into the pgstats subsystem (see NumBackendStatSlots). 
This can probably be reorganized, but I didn't pursue it further.

Now, I'm a sucker for refactoring, but I feel this proposal is going 
into a direction I don't understand.  I'd prefer that we focus around 
building out background workers as the preferred subprocess mechanism. 
Building out a second generic mechanism, again, I don't understand the 
direction.  Are we hoping to add more of these processes?  Make it 
extensible?  The net lines added/removed by this patch series seems 
pretty neutral.  What are we getting at the end of this?

More specifically, I don't agree with the wholesale renaming of 
auxiliary process to subprocess.  Besides the massive code churn, the 
old naming seemed pretty good to distinguish them from background 
workers, the new naming is more ambiguous.

Btw., if I had a lot of time I would attempt to rewrite walreceiver and 
perhaps the autovacuum system as background workers and thus further 
reduce the footprint of the aux process system.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services