merge CASSANDRA-2558 from 0.8

git-svn-id: https://svn.apache.org/repos/asf/cassandra/trunk@1097889 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -17,6 +17,7 @@
  * fix incorrect use of NBHM.size in ReadCallback that could cause
    reads to time out even when responses were received (CASSAMDRA-2552)
  * trigger read repair correctly for LOCAL_QUORUM reads (CASSANDRA-2556)
+ * Allow configuring the number of compaction thread (CASSANDRA-2558)
 
 
 0.8.0-beta1

conf/cassandra.yaml

@@ -249,10 +249,15 @@ column_index_size_in_kb: 64
 # will be logged specifying the row key.
 in_memory_compaction_limit_in_mb: 64
 
-# Enables multiple compactions to execute at once. This is highly recommended
-# for preserving read performance in a mixed read/write workload as this
-# avoids sstables from accumulating during long running compactions.
-compaction_multithreading: false
+# Number of compaction threads. This default to the number of processors,
+# enabling multiple compactions to execute at once. Using more than one
+# thread is highly recommended to preserve read performance in a mixed
+# read/write workload as this avoids sstables from accumulating during long
+# running compactions. The default is usually fine and if you experience
+# problems with compaction running too slowly or too fast, you should look at
+# compaction_throughput_mb_per_sec first.
+# Uncomment to make compaction mono-threaded.
+#concurrent_compacters: 1
 
 # Throttles compaction to the given total throughput across the entire
 # system. The faster you insert data, the faster you need to compact in

src/java/org/apache/cassandra/config/Config.java

@@ -82,7 +82,7 @@ public class Config
     /* if the size of columns or super-columns are more than this, indexing will kick in */
     public Integer column_index_size_in_kb = 64;
     public Integer in_memory_compaction_limit_in_mb = 256;
-    public Boolean compaction_multithreading = true;
+    public Integer concurrent_compactors = Runtime.getRuntime().availableProcessors();
     public Integer compaction_throughput_mb_per_sec = 16;
     
     public String[] data_file_directories;

src/java/org/apache/cassandra/config/DatabaseDescriptor.java

@@ -341,8 +341,11 @@ public class DatabaseDescriptor
                 throw new ConfigurationException("in_memory_compaction_limit_in_mb must be a positive integer");
             }
 
-            if (conf.compaction_multithreading == null)
-                conf.compaction_multithreading = true;
+            if (conf.concurrent_compactors == null)
+                conf.concurrent_compactors = Runtime.getRuntime().availableProcessors();
+
+            if (conf.concurrent_compactors <= 0)
+                throw new ConfigurationException("concurrent_compactors should be strictly greater than 0");
 
             if (conf.compaction_throughput_mb_per_sec == null)
                 conf.compaction_throughput_mb_per_sec = 16;
@@ -729,9 +732,9 @@ public class DatabaseDescriptor
         return conf.in_memory_compaction_limit_in_mb * 1024 * 1024;
     }
 
-    public static boolean getCompactionMultithreading()
+    public static int getConcurrentCompactors()
     {
-        return conf.compaction_multithreading;
+        return conf.concurrent_compactors;
     }
 
     public static int getCompactionThroughputMbPerSec()

src/java/org/apache/cassandra/db/CompactionManager.java

@@ -1212,9 +1212,7 @@ public class CompactionManager implements CompactionManagerMBean
 
         private static int getThreadCount()
         {
-            if (!DatabaseDescriptor.getCompactionMultithreading())
-                return 1;
-            return Math.max(2, Runtime.getRuntime().availableProcessors());
+            return Math.max(1, DatabaseDescriptor.getConcurrentCompactors());
         }
 
         void beginCompaction(CompactionInfo.Holder ci)