HBASE-13008 Better default for hbase.regionserver.regionSplitLimit parameter (Srikanth Srungarapu)

hbase-common/src/main/resources/hbase-default.xml

@@ -333,6 +333,15 @@ possible configurations would overwhelm and obscure the important.
       DelimitedKeyPrefixRegionSplitPolicy, KeyPrefixRegionSplitPolicy etc.
     </description>
   </property>
+  <property>
+    <name>hbase.regionserver.regionSplitLimit</name>
+    <value>1000</value>
+    <description>
+      Limit for the number of regions after which no more region splitting should take place.
+      This is not hard limit for the number of regions but acts as a guideline for the regionserver
+      to stop splitting after a certain limit. Default is set to 1000.
+    </description>
+  </property>
 
   <!--ZooKeeper configuration-->
   <property>

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/CompactSplitThread.java

@@ -76,6 +76,10 @@ public class CompactSplitThread implements CompactionRequestor, PropagatingConfi
   public final static String MERGE_THREADS = "hbase.regionserver.thread.merge";
   public final static int MERGE_THREADS_DEFAULT = 1;
 
+  public static final String REGION_SERVER_REGION_SPLIT_LIMIT =
+      "hbase.regionserver.regionSplitLimit";
+  public static final int DEFAULT_REGION_SERVER_REGION_SPLIT_LIMIT= 1000;
+  
   private final HRegionServer server;
   private final Configuration conf;
 
@@ -98,8 +102,8 @@ public class CompactSplitThread implements CompactionRequestor, PropagatingConfi
     super();
     this.server = server;
     this.conf = server.getConfiguration();
-    this.regionSplitLimit = conf.getInt("hbase.regionserver.regionSplitLimit",
+    this.regionSplitLimit = conf.getInt(REGION_SERVER_REGION_SPLIT_LIMIT,
-        Integer.MAX_VALUE);
+        DEFAULT_REGION_SERVER_REGION_SPLIT_LIMIT);
 
     int largeThreads = Math.max(1, conf.getInt(
         LARGE_COMPACTION_THREADS, LARGE_COMPACTION_THREADS_DEFAULT));
@@ -427,6 +431,10 @@ public class CompactSplitThread implements CompactionRequestor, PropagatingConfi
   }
 
   private boolean shouldSplitRegion() {
+    if(server.getNumberOfOnlineRegions() > 0.9*regionSplitLimit) {
+      LOG.warn("Total number of regions is approaching the upper limit " + regionSplitLimit + ". "
+          + "Please consider taking a look at http://hbase.apache.org/book.html#ops.regionmgt");
+    }
     return (regionSplitLimit > server.getNumberOfOnlineRegions());
   }