Using Bulk Operations with Coherence Off-Heap Storage
By jpurdy on May 31, 2012
Some NamedCache methods (including clear(), entrySet(Filter), aggregate(Filter, …), invoke(Filter, …)) may generate large intermediate results. The size of these intermediate results may result in out-of-memory exceptions on cache servers, and in some cases on cache clients. This may be particularly problematic if out-of-memory exceptions occur on more than one server (since these operations may be cluster-wide) or if these exceptions cause additional memory use on the surviving servers as they take over partitions from the failed servers. This may be particularly problematic with clusters that use off-heap storage (such as NIO or Elastic Data storage options), since these storage options allow greater than normal cache sizes but do nothing to address the size of intermediate results or final result sets.
One workaround is to use a PartitionedFilter, which allows the application to break up a larger operation into a number of smaller operations, each targeting either a set of partitions (useful for reducing the load on each cache server) or a set of members (useful for managing client result set sizes).
It is also possible to return a key set, and then pull in the full entries using that key set. This also allows the application to take advantage of near caching, though this may be of limited value if the result is large enough to result in near cache thrashing.