Date: Sat, 21 Mar 2020 09:30:44 +0100
From: Kurt Roeckx <kurt@roeckx.be>
To: Rui DeSousa <rui@crazybean.net>
Cc: pgsql-admin@lists.postgresql.org
Subject: Re: Append only tables
Message-ID: <20200321083044.GI22330@roeckx.be>
References: <20200320215053.GH22330@roeckx.be>
 <7CBBAB2A-A8C4-47D6-9912-7B3AD6554EAF@crazybean.net>
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On Sat, Mar 21, 2020 at 01:44:47AM -0400, Rui DeSousa wrote:
> 
> 
> > On Mar 20, 2020, at 5:50 PM, Kurt Roeckx <kurt@roeckx.be> wrote:
> > 
> > Hi,
> > 
> > I have a few tables that are append only. Thre are only gets insert
> > and select queries, never update or delete.
> > 
> > What I see is that every file is still being updated. It's
> > currently about 500 GB big, and every of that almost 500 files has
> > been touched the past 24 hours.
> > 
> > (auto) vacuum is not happening on the table.
> > 
> 
> Vacuum is still required as the tuples need to be frozen.  Have you vacuumed the table?

I did not manually vacuum them, nor did auto vacuum ever get
triggered, at least not according to what is in
pg_stat_user_tables;

> It could be the result of records being frozen during selects statements; select can freeze tuples that meet the criteria for being frozen. 

I guess it's doing that now. iotop shows:
  TID  PRIO  USER    DISK READ>  DISK WRITE  SWAPIN      IO COMMAND
10227 be/4 postgres     67.68 G     67.56 G  0.00 % 79.66 % postgres: 12/main: kurt certs [local] VACUUM

> I would recommend vacuuming the table to get the existing records frozen; then I believe you should see fewer updates to the all the base files.

If this is needed, why doesn't autovacuum do this for me? Or do I
need to modify some parameters so that autovacuum does get
triggered?

I actually didn't run any select query on that table yet, it's
still importing the data. Can an insert also trigger the freeze?


Anyway, the vacuum is running, I will let you know if it helps or
not.


Kurt