LARGE single-system Cyrus installs?

[Rob Mueller]

> About 30% of all I/O is to mailboxes.db, most of which is read.  I
> haven't personally deployed a split-meta configuration, but I
> understand the meta files are similarly heavy I/O concentrators.

That sounds odd.

Given the size and "hotness" of mailboxes.db, and in most cases the size of 
mailboxes.db compared to the memory your machine has, basically the OS 
should end up caching the entire thing in memory. If it has to keep going 
back to disk to get parts of it, it suggests something is wrong with the OS 
caching eviction policy.

I wonder if it's worth setting up a separate process that just mmaps the 
whole file and then uses mlock() to keep the pages in memory, that should 
mean it removes all read IO for mailboxes.db.

Rob