[ext] 2.3.7 slower than 2.3.6?

[Timo Sirainen]

On 16 Jul 2019, at 11.15, Ralf Hildebrandt via dovecot <dovecot at dovecot.org> wrote:
> 
> * Timo Sirainen via dovecot <dovecot at dovecot.org>:
> 
>>> And alas, I had a look at the monitoring and found that disk IO has
>>> increase A LOT after the update: https://www.arschkrebs.de/images/dovecot-disk-io-increase.png
>>> 
>>> I zoomed in and found that the sudden increace in IO coincides with
>>> the update to 2.3.7 (14:35): https://www.arschkrebs.de/images/dovecot-io-2.png <https://www.arschkrebs.de/images/dovecot-io-2.png>
>> 
> 
>> Do the different disks have different kinds of data? 
> 
> All of the data is an /dev/sda1

What filesystem is this?

I did a bunch of testing, and after initially thinking I saw an increase it was just due to bad testing because the new TCP_NODELAY changes allowed imaptest to do more work. So I can't see that there is any disk IO difference.

There are a few intentional changes to lib-index and also mdbox code. One of those is that dovecot.index.cache files are being recreated more often now. In some cases they were wasting a lot of disk space because expunged mails hadn't been removed from them. I guess it's a possibility that all the disk IO was because in your system Dovecot started recreating all those files at the same time. Maybe you could try upgrading again during slower hours and see if the disk IO normalizes after a while?