Cyrus infrastructure performance less than expected
robm at fastmail.fm
Tue Apr 29 03:48:23 EDT 2008
> 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
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.
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