Even without transactions, multiple threads can safely access/modify the entry concurrently. Optimistic vs. pessimistic locking is relevant to transactions only, though, because this involves lock handling for transactions that can often take seconds. In non-tx setup the locks are acquired only for brief moments (milliseconds) internally, and distinction pessimistic/optimistic does not make sense here.
The real difference is that in transaction you can modify different entries ~atomically.
Thanks for your valuable reply.
Does infinispan remote cache supports transaction?
like hotrod client
Not at this moment, but it's being actively developed these days. [ISPN-7807] Hot Rod Lightweight Transaction (Synchronization) - JBoss Issue Tracker
You can expect this to be in 9.2 (fall 2017) - no promises ofc.