[infinispan-dev] A couple of general eviction questions

[Alex Kluge]

Hi,

  I have a couple of general questions about eviction.

Why is it an out of band process? From http://community.jboss.org/wiki/infinispan-eviction it looks like the eviction thread is trimming the data container to its size limit.  I created an interceptor and used a clock mechanism (as in clock cache) to determine when elements should be removed from the cache. It is positioned just after the mvcc locking and if there are enough keys in a node, then one is removed. The performance impact here is reasonable, but the clock is much faster than a strict LRU. It also removes the possibility of the OOM when you don't run the eviction thread frequently enough. The LIRS implementation also looks reasonably fast, and so could be in lined into the cache access. With a flatter cache does it make sense for eviction to be inline?


Has any thought been given to placing an explicit limit on the amount of memory that is used? You can dynamically fetch the old generation max size at startup, then set a notification on the corresponding mbean to notify you when a threshold is exceeded. As long as memory usage remains above a limit, entries can be evicted from the cache. Once it falls below the limit, the check no longer needs to be made until the notification triggers again. This is a bit course as it looks at the total memory in use, but Java doesn't have a sizeof operator. I went down this path because the general eviction path can run into issues if the maxentries is too large.

                                            Alex