Cyrus infrastructure performance less than expected

[Rob Mueller]

> On current production platform the frontends use swap massively but the
> impact is far less than on the new platform.

It's not so much how much swap is actually used, but how much is being paged 
in or paged out at any time. If there are memory pages not being used at 
all, the OS will swap them out, but that's fine because they're not being 
used.

The problem is when more memory pages are being used than memory available. 
In that case the OS starts continuously moving things back and forth between 
RAM and swap, which causes performance to become horrible.

Can you run "free" and "vmstat 10 10" (will take 100 seconds to run) on one 
of your old frontends and one of your new frontends during peak times so we 
can get an idea of what is going on with memory + swap.

Also lets just confirm a process count on your system. Run these commands:

ps ax | wc -l
ps ax | grep imapd | wc -l

On both old and new.

> We are indeed using 64bits OS and 64bits software. This is the main
> difference between the old platform which runs a 32 bits software on a
> 32 bits OS.

That will increase memory usage as well. Every pointer in the system (either 
in the kernel or in an application) is now using twice as much space. Of 
course not all data is pointers, but depending on the application it can 
mean considerably more memory is used.

Lets start with the free, vmstat and ps data, and we'll go from there.

Rob