From f59035fd6a3667b5cf1124edea9bacf78bdfff5e Mon Sep 17 00:00:00 2001
From: petetanton <pete.tanton@bbc.co.uk>
Date: Mon, 8 Jan 2018 11:20:45 +0000
Subject: [PATCH] new ReadFrom with a randomly order list of slaves

---
 .../com/lambdaworks/redis/ReadFromImpl.java   | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/src/main/java/com/lambdaworks/redis/ReadFromImpl.java b/src/main/java/com/lambdaworks/redis/ReadFromImpl.java
index 1cf86c5ad8..3418bcea47 100644
--- a/src/main/java/com/lambdaworks/redis/ReadFromImpl.java
+++ b/src/main/java/com/lambdaworks/redis/ReadFromImpl.java
@@ -18,6 +18,7 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Random;
 
 import com.lambdaworks.redis.internal.LettuceLists;
 import com.lambdaworks.redis.models.role.RedisInstance;
@@ -121,6 +122,36 @@ public List<RedisNodeDescription> select(Nodes nodes) {
         }
     }
 
+    /**
+     * Read from master and slaves. Prefer slave reads and fall back to master if the no slave is not available. Order slaves randomly.
+     */
+    static final class ReadFromRandomSlavePreferred extends ReadFrom {
+
+        private final Random rnd = new Random(System.nanoTime());
+
+        @Override
+        public List<RedisNodeDescription> select(Nodes nodes) {
+
+            List<RedisNodeDescription> result = new ArrayList<>(nodes.getNodes().size());
+
+            for (RedisNodeDescription node : nodes) {
+                if (node.getRole() == RedisInstance.Role.SLAVE) {
+                    result.add(node);
+                }
+            }
+
+            Collections.shuffle(result, rnd);
+
+            for (RedisNodeDescription node : nodes) {
+                if (node.getRole() == RedisInstance.Role.MASTER) {
+                    result.add(node);
+                }
+            }
+
+            return result;
+        }
+    }
+
     /**
      * Read from nearest node.
      */