OLAP Saiku Cache expires

Question

I'm using Saiku and PHPAnalytics to run MDX queries on my cube. it seems if i run queries it's all good, caching is fine. But if I go for 2 hours and run those queries again - it does not using cache! Why? I need the cache to be saved for a long time! What to do? I tried to add this ti mondrian.properties mondrian.rolap.CachePool.costLimit = 2147483647

But no help. What do to?

Answer 1

The default in-memory cache of Mondrian stores things in a WeakHashMap. This means that it could be cleared at the discretion of the JVM's garbage collector. Most application servers are setup to do a periodical sweep of garbage collection (usually each hour or so). You have to either tweak your JVM's configuration to not do this.

-Dsun.rmi.dgc.client.gcInterval=3600000 -Dsun.rmi.dgc.server.gcInterval=3600000

You can also implement your own cache implementation of the SegmentCache SPI. If your implementation uses hard references, they will never be collected. This is trickier to do and will require you to do quite a bit of studying to get it right. You can start by taking a look at the default implementation and start from there.

Answer 2

The mondrian cache should cache up until the cache is deliberately flushed. That said it uses an aging system to determine what should be cached should it run out of memory to store the data, the oldest query gets pushed out of the cache and replaced.

I've not tried the PHPAnalytics stuff, but maybe they've put some call into the Saiku server to flush the cache on a regular basis, otherwise this shouldn't happen.