Some worth mentioning improvements for pessimistic transactions

Pessimistic transactions were added in 5.1 and are the "rebranding" of eager transactions from previous Infinispan releases. But besides the re-branding, the code also brought some worth mentioning performance optimisation:

• a single RPC happens for acquiring lock on a key, disregarding the number of invocations. So if you call cache.put(k,v) in a loop, within the scope of the same transaction, there is only one remote call to the owner of k.
• if the key you want to lock/write maps to the local node then no remote locks are acquired. In other words there won't be any RPCs for writing to a key that maps locally. This can be very powerful used in conjunction with the KeyAffinityService, as it allows you to control the locality of you keys.
• during the two phase commit (2PC), the prepare phase doesn't perform any RPCs: this optimisation is based on the fact locks are already acquired on each write. This means that then number of RPCs during transactions lifespan is reduced with 1.
• for some writes to the cache (e..g cache.put(k,v)) two RPCs were performed: one to acquire the remote lock and one to fetch the previous value. The obvious optimisation in this case was to make a single RPC for both operations - which we do starting with 5.1.

Enjoy!

Mircea