[TINKERPOP-1125] RoundRobin load balancing always uses the second Host when size = 2

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Done
• Affects Version/s: 3.1.0-incubating
• Fix Version/s: 3.2.0-incubating, 3.1.2-incubating
• Component/s: driver
• Assignee: Stephen Mallette
• Reporter: Kieran Sherlock
• Created: 04/Feb/16 21:32
• Updated: 22/Feb/16 13:31
• Resolved: 22/Feb/16 13:31

Description

Bring up two gremlin-server
Create a Cluster with these two servers, by default LoadBalancingStrategy.RoundRobin() is used.
Create a client and make queries.
Notice that all requests go to the second server.

this.cluster.loadBalancingStrategy().select(msg).next() is called twice in Client.chooseConnection(), so always the second Host is used.

The following seems to work

Unable to find source-code formatter for language: diff. Available languages are: actionscript, ada, applescript, bash, c, c#, c++, cpp, css, erlang, go, groovy, haskell, html, java, javascript, js, json, lua, none, nyan, objc, perl, php, python, r, rainbow, ruby, scala, sh, sql, swift, visualbasic, xml, yaml

diff --git a/gremlin-driver/src/main/java/org/apache/tinkerpop/gremlin/driver/Client.java b/gremlin-driver/src/main/java/org/apache/tinkerpop/gremlin/driver/Client.java
index 8c80b8a..17c9a99 100644
--- a/gremlin-driver/src/main/java/org/apache/tinkerpop/gremlin/driver/Client.java
+++ b/gremlin-driver/src/main/java/org/apache/tinkerpop/gremlin/driver/Client.java
@@ -341,7 +341,7 @@ public abstract class Client {
             final Iterator<Host> possibleHosts = this.cluster.loadBalancingStrategy().select(msg);
             if (!possibleHosts.hasNext()) throw new TimeoutException("Timed out waiting for an available host.");

-            final Host bestHost = this.cluster.loadBalancingStrategy().select(msg).next();
+            final Host bestHost = possibleHosts.next();
             final ConnectionPool pool = hostConnectionPools.get(bestHost);
             return pool.borrowConnection(cluster.connectionPoolSettings().maxWaitForConnection, TimeUnit.MILLISECONDS);
         }

Issue Links

• relates to: TINKERPOP-1126 A single Host spawns many reconnect tasks
• relates to: TINKERPOP-1127 client fails to reconnect to restarted server