Message-ID: <1524809191.2382.4.camel@cybertec.at>
Subject: Re: vacuumdb causes memory drain.
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Sushil Shirodkar <sushilps@hotmail.com>, Don Seiler <don@seiler.us>
Cc: "pgsql-admin@postgresql.org" <pgsql-admin@postgresql.org>
In-Reply-To: 
 <BL0PR0102MB3410F730EA8CE5F0C2A19CACD48E0@BL0PR0102MB3410.prod.exchangelabs.com>
References: 
	<BL0PR0102MB341015831D5ECBAF95D7966FD48E0@BL0PR0102MB3410.prod.exchangelabs.com>
	,<CAHJZqBCr0Xyp_58iXpknrTrXQFoYc3BPCqY8G0h-STzaMWLsqQ@mail.gmail.com>
	 <BL0PR0102MB3410F730EA8CE5F0C2A19CACD48E0@BL0PR0102MB3410.prod.exchangelabs.com>
Organization: Cybertec
Content-Type: text/plain; charset="UTF-8"
Date: Fri, 27 Apr 2018 08:06:31 +0200
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

Sushil Shirodkar wrote:

> > On Thu, Apr 26, 2018 at 10:31 AM, Sushil Shirodkar <sushilps@hotmail.com> wrote:
> > > Running "vacuumdb -a -z -v" from the cron on one of our test environment, and 
> > > noticed that memory of the server goes down from 3.4GB free to 150MB.  Once 
> > > the process is over, memory is not released, is it normal or something needs to be 
> > > changed ? also other processes start running slow afterwards due to low memory.  
> >
> > How are you measuring free memory? Memory might be listed in cached/buffers instead of
> > free but is still available. Although that wouldn't then explain other processes being slow.
>
> I have put some small script which runs in a loop with "free -h" command,
> while I am running "vacuumdb".  Once I clear by "sync" or bounce PG,
> everything runs normal afterward.

Then I would say everything is fine.
It is normal for a Linux system to have almost no free memory; the memory is used
for the file system cache.

Do you experience any problems, like reduced performance or high I/O?

Yours,
Laurenz Albe
-- 
Cybertec | https://www.cybertec-postgresql.com