[horde] Horde performance with ActiveSync?

[Sebastian Arcus]

I have a Horde 5.2.17 + PHP 5.6.35 + Postgresql 9.2 + Lighttpd 1.4.49 
with 10 iPhones/iPads in ActiveSync/Exchange mode. The users have fairly 
large Inboxes - some of them of 20 000+ emails. On IMAP that is not 
causing any issues, and hardly any load on the server.

It is the first setup I am doing with more than 1-2 devices in Exchange 
mode, and I am trying to get a sense of what performance is 'normal' or 
expected.

The server is only an Intel Core2 4400, with not too much other load on 
it, but since configuring Horde with ActiveSync it is spending almost 
all the time with 2-3 php-cgi processes, each with 30%-50% cpu core 
load. There is virtually no access through the Horde web interface, so 
it seems to me that these php-cgi processes are serving exclusively 
ActiveSync sessions.

I know it can be a vague question, or at least one with a complex 
answer, but would anybody with experience in running Horde with 
ActiveSync say that the above load sounds about right? I have 
implemented as many of the Horde tuning tips I could implement so far - 
and I am happy to look into tweaking things further. But if ActiveSync 
with Horde is just heavy on the cpu anyway, I will just look into 
upgrading the hardware.

Any advice gratefully appreciated.