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From "Thomas Mueller" <thomas.tom.muel...@gmail.com>
Subject CacheManager (Memory Management in Jackrabbit)
Date Thu, 02 Nov 2006 08:51:45 GMT
Hi,

Just recently I experienced an out of memory problem with Jackrabbit.
I analyzed the memory usage and found the problem is the combined size
of the various caches of Jackrabbit, and other libraries (Lucene, the
database, and others). The biggest problem was the combined size of
the o.a.j.core.state.MLRUItemStateCache caches. Each session seems to
create a few (?) of those caches, and each one is limited to 4 MB by
default. At one point, I had 16 of those. 64 MB is not that much, but
if you only allocate 128 MB it is already a problem. It is possible to
change the size limit (by changing DEFAULT_MAX_MEM), but this means
the biggest one can get at most this amount of memory.

I think that would be good is some kind of dynamic (cache-) memory
management. A single service that distributes the available memory (or
at least some fixed amount) dynamically to all those caches (let's
call it CacheManager). This could be per-repository, or a singleton.
It would keep a weak reference to all caches. If a new cache is
created, the cache manager would give him some minimum amount of
memory (let's say 128 KB), and if the cache is used frequently, it
would get more memory. The cache manager would shrink caches that are
not used frequently.

I suggest to implement such a singleton CacheManager. Currently just
for MLRUItemStateCache, as this seems to be the biggest problem so
far. Later on (if we think it's worth doing it), it could be extended
to other caches as well.

Maybe such a service already exists somewhere (apache commons?) Please
tell me if you know of any such service. If not, I will go ahead and
implement such a feature, unless there are other ideas.

Thomas

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