On 2/21/2013 8:27 AM, Patrick Raspante wrote:
Is it required (or at least suggested) that multi-mastered directory
server instances have the equal values for dbcache and entry cache
settings? If so, what adverse effects result from not configuring the
caches similarly?
There's no relationship like the one you're suggesting. You can
configure any size for each kind of cache.
These days, (now that computers are so much bigger and faster than when
the DS was originally designed), unless you're looking for the last
fraction of performance from your deployment, I'd suggest leaving the
cache sizes at the default. This will push most of the caching down into
the filesystem, which will do a reasonably good job with the big benefit
that you won't need to spend time worrying about and futzing with the
cache sizing.
Remember that the entry cache holds entry content (not index data), in
memory, in the "decoded state".
So if you're looking to serve 10's of thousands of entries per second
from a server, it helps to have them in the entry cache because you're
saving the cost to read the entry data from the filesystem cache and
decode it from ascii ldif to the avl tree memory format. This might
amount to 1us or more per entry, for every entry touched that is not
found in the entry cache.
The DB cache by contrast holds pages of database content (entries + any
referenced index data) in memory. So it saves (only) the cost to copy
the page from the filesystem cache - the payload data is just a copy of
the on-disk data.