kvserver: add TODO for using a cheaper batch

Epic: none
Release note: none

Author: pav-kv

pkg/kv/kvserver/replica_application_state_machine.go

@@ -143,6 +143,9 @@ func (sm *replicaStateMachine) NewBatch() apply.Batch {
 	// make it safer.
 	b.r = r
 	b.applyStats = &sm.applyStats
+	// TODO(#144627): most commands do not need to read. Use NewWriteBatch because
+	// it is more efficient. If there are exceptions, sparingly use NewReader or
+	// NewBatch (if it needs to read its own writes, which is unlikely).
 	b.batch = r.store.TODOEngine().NewBatch()
 	r.mu.RLock()
 	b.state = r.shMu.state