From b1f9fd39f50a8fb8bf18625e3bab6f616a859bb0 Mon Sep 17 00:00:00 2001
From: Ruban Monu <rmonu@twitter.com>
Date: Mon, 8 Dec 2014 11:13:10 -0800
Subject: [PATCH] Read through store - do not query backing store when no cache
 miss

---
 .../twitter/storehaus/ReadThroughStore.scala    | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/storehaus-core/src/main/scala/com/twitter/storehaus/ReadThroughStore.scala b/storehaus-core/src/main/scala/com/twitter/storehaus/ReadThroughStore.scala
index 874d2b6d..cbd9646d 100644
--- a/storehaus-core/src/main/scala/com/twitter/storehaus/ReadThroughStore.scala
+++ b/storehaus-core/src/main/scala/com/twitter/storehaus/ReadThroughStore.scala
@@ -72,12 +72,17 @@ class ReadThroughStore[K, V](backingStore: ReadableStore[K, V], cache: Store[K,
         val hits = responses.filter { !_._2.isEmpty }
         val missedKeys = responses.filter { _._2.isEmpty }.keySet
 
-        FutureOps.mapCollect(backingStore.multiGet(missedKeys ++ failedKeys)).flatMap { storeResult =>
-          // write fetched keys to cache, best effort
-          mutex.acquire.flatMap { p =>
-            FutureOps.mapCollect(cache.multiPut(storeResult))(FutureCollector.bestEffort[(K1, Unit)])
-              .map { u => hits ++ storeResult }
-              .ensure { p.release }
+        val remaining = missedKeys ++ failedKeys
+        if (remaining.isEmpty) {
+          Future.value(hits) // no cache misses
+        } else {
+          FutureOps.mapCollect(backingStore.multiGet(remaining)).flatMap { storeResult =>
+            // write fetched keys to cache, best effort
+            mutex.acquire.flatMap { p =>
+              FutureOps.mapCollect(cache.multiPut(storeResult))(FutureCollector.bestEffort[(K1, Unit)])
+                .map { u => hits ++ storeResult }
+                .ensure { p.release }
+            }
           }
         }
       }