Lisa Giacchetti <[EMAIL PROTECTED]> writes:
> sizes and number of files. Finally since we had enough memory to do so, we
> increased the amount of cache kept in memory. This instantly improved the
> situtation. The current config we are running with is:
>
> GRANDE="-stat 2800 -dcache 4608 -daemons 7 -volumes 256"
>
> From my notes I have down that dcache indicates the number of cache item
> entries you want cached in memory. We set this to 75% of the # of vfiles
> in the cache. There is a formula we used to figure out the # of vfiles
> in the cache
dcache structures are "chunk descriptors", and don't actually contain
data. They are in fact a cache of the "CacheItems" file which lives in
the data cache directory (/usr/vice/cache). This descriptor is fairly
small, but must be in memory before the data from its chunk can be read
or written. The tradeoff is that these dcaches are often accessed via
a hash table with linked-lists of overflow buffers, so if the
linked-lists become _very_ large, it becomes expensive to touch
new chunks.
Your configuration suggests that you have relatively few, large files,
and the default chunk size of 64K. Did you try using "-dcache 2304
-chunk 17" ?
75% of the vfiles in the cache seems high unless all the vfiles are in
use. Usually, only about 50-75% of the vfiles are used.
> the tuning of the parameters above and finally had a Transarc consultant
> come to our site for a two day consulting stint ($$). He helped us tune the
> cache parameters to what we have above, in about a half hour. This is just a
> strong pitch for more technical assistance on issues like this via phone
> support.
There are a few standard suggestions that can be made, but they pretty
much amount to using the appropriate rc.* file. Other than that, it
becomes something like the story of the refigerator repairman: "$5 for
hitting it, $95 for knowing _where_ to hit it." It really takes a lot
of experience to do this quickly -- and even despite that, finding the
OPTIMUM settings for unusual configurations requires repeated
experiments.
You shouldn't hold this against the phone support folks, it's really
outside their job description.
