Set the number of goroutines for gentle merging to 18. It is little slower to...

Set the number of goroutines for gentle merging to 18. It is little slower to run these goroutines, but they keep the memory usage in check.

posting/lists.go

@@ -182,9 +182,9 @@ func checkMemoryUsage() {
 		} else {
 			// If merging is slow, we don't want to end up having too many goroutines
 			// merging the dirty list. This should keep them in check.
-			// With a value of 12 and duration of 5 seconds, some goroutines are
-			// taking over a minute to finish.
-			if mr.Count() > 12 {
+			// With a value of 18 and duration of 5 seconds, some goroutines are
+			// taking over 1.5 mins to finish.
+			if mr.Count() > 18 {
 				glog.Info("Skipping gentle merging.")
 				continue
 			}