Re: INSERT - UPDATE throughput oscillating and SSD activity after stopping the client

On Tue, Dec 6, 2016 at 2:44 AM, Tom DalPozzo <t(dot)dalpozzo(at)gmail(dot)com> wrote:

> Hi,
> about SSD light:
>

> I guessed it was WAL -> actual db files data traffic. It explains why the
> light stops blinking after shutting down the server (I did it via kill
> command) .
>

Do you kill with -15 (the default) or -9? And which process, the postgres
master itself or just some random child?

> But if so, I expected the light to restart blinking after restarting
> the server (in order to continue WAL->db activity).
>

The normal checkpoint is paced. So trickling out data slowly will keep the
light on, but not actually stress the system.

When you shutdown the system, it does a fast checkpoint. This gets the
data written out as quickly as possible (since you are shutting down, it
doesn't worry about interfering with performance for other users, as there
are none), so once it is done you don't see the light anymore. If you do a
clean shutdown (kill -15 of the postgres master) this fast checkpoint
happens upon shutdown. If you do an abort (kill -9) then the fast
checkpoint happens upon start-up, once recovery is finished but before the
database is opened of regular use.

Cheers,

Jeff