Merge pull request #426 from metamx/allow-disabling-opqueue

Disable memcached op-queue bound by default

server/src/main/java/io/druid/client/cache/MemcachedCache.java

@@ -32,6 +32,8 @@ import net.spy.memcached.FailureMode;
 import net.spy.memcached.MemcachedClient;
 import net.spy.memcached.MemcachedClientIF;
 import net.spy.memcached.internal.BulkFuture;
+import net.spy.memcached.ops.LinkedOperationQueueFactory;
+import net.spy.memcached.ops.OperationQueueFactory;
 import org.apache.commons.codec.digest.DigestUtils;
 
 import javax.annotation.Nullable;
@@ -56,7 +58,15 @@ public class MemcachedCache implements Cache
 
       // always use compression
       transcoder.setCompressionThreshold(0);
-      MemcachedOperationQueueFactory queueFactory = new MemcachedOperationQueueFactory(config.getMaxOperationQueueSize());
+
+      OperationQueueFactory opQueueFactory;
+      long maxQueueBytes = config.getMaxOperationQueueSize();
+      if(maxQueueBytes > 0) {
+        opQueueFactory = new MemcachedOperationQueueFactory(maxQueueBytes);
+      } else {
+        opQueueFactory = new LinkedOperationQueueFactory();
+      }
+
       return new MemcachedCache(
         new MemcachedClient(
           new ConnectionFactoryBuilder().setProtocol(ConnectionFactoryBuilder.Protocol.BINARY)
@@ -68,7 +78,7 @@ public class MemcachedCache implements Cache
                                         .setShouldOptimize(true)
                                         .setOpQueueMaxBlockTime(config.getTimeout())
                                         .setOpTimeout(config.getTimeout())
-                                        .setOpQueueFactory(queueFactory)
+                                        .setOpQueueFactory(opQueueFactory)
                                         .build(),
           AddrUtil.getAddresses(config.getHosts())
         ),

server/src/main/java/io/druid/client/cache/MemcachedCacheConfig.java

@@ -25,19 +25,28 @@ import javax.validation.constraints.NotNull;
 
 public class MemcachedCacheConfig
 {
+  // default to 30 day expiration for cache entries
+  // values greater than 30 days are interpreted by memcached as absolute POSIX timestamps instead of duration
   @JsonProperty
-  private int expiration = 2592000; // What is this number?
+  private int expiration = 30 * 24 * 3600;
+
   @JsonProperty
   private int timeout = 500;
+
+  // comma delimited list of memcached servers, given as host:port combination
   @JsonProperty
   @NotNull
   private String hosts;
+
   @JsonProperty
   private int maxObjectSize = 50 * 1024 * 1024;
+
   @JsonProperty
   private String memcachedPrefix = "druid";
+
+  // maximum size in bytes of memcached client operation queue. 0 means unlimited
   @JsonProperty
-  private long maxOperationQueueSize = 256 * 1024 * 1024L; // 256 MB
+  private long maxOperationQueueSize = 0;
 
   public int getExpiration()
   {