Major Description
Currently we measure the metric GLOBAL_MUTATION_COMMIT_TIME as the time spent just in htable.batch rpc for base and index tables. https://github.com/apache/phoenix/blob/master/phoenix-core/src/main/java/org/apache/phoenix/execute/MutationState.java#L1029-L1136
We don't measure the time spent in MutationState#validateAndGetServerTimestamp which makes rpc to SYSTEM.CATALOG table and which is a part of commit phase.