MB-44764 Re-order config check and checkInterval() evaluations

The checkInterval method calls isInitial() which inturn iterates
over entire list of instances to see if there is any instance
belonging to the streamId and keyspaceId on which flush was done.

With 10000 indexes on a node, iterating over all 10000 indexes
for every flushDone is a costly call. This can be avoided when
writer tuning is not enabled. Hence, re-ordering the checks
so that we skip the iteration of 10000 indexes

Change-Id: I0b96960dbe8d1375fdf62d409d97d84a82027384

secondary/indexer/storage_manager.go

@@ -505,6 +505,10 @@ func (s *storageMgr) flushDone(streamId common.StreamId, keyspaceId string,
 			return true
 		}
 
+		// TODO (Collections): It is not optimal to iterate over
+		// entire instIdList when there are large number of indexes on
+		// a node in MAINT_STREAM. This logic needs to be optimised further
+		// when writer tuning is enabled
 		for _, instId := range instIdList {
 			inst, ok := indexInstMap[instId]
 			if ok && inst.Stream == streamId &&
@@ -528,8 +532,8 @@ func (s *storageMgr) flushDone(streamId common.StreamId, keyspaceId string,
 
 	if common.GetStorageMode() == common.PLASMA {
 
-		if time.Now().UnixNano()-s.lastFlushDone > checkInterval() &&
-			s.config["plasma.writer.tuning.enable"].Bool() {
+		if s.config["plasma.writer.tuning.enable"].Bool() &&
+			time.Now().UnixNano()-s.lastFlushDone > checkInterval() {
 
 			var wg sync.WaitGroup