From 2d214ccc52d7fd321c4ced1960d11d719b53b4e5 Mon Sep 17 00:00:00 2001
From: Michael Stack <stack@apache.org>
Date: Fri, 30 Jul 2010 04:57:44 +0000
Subject: [PATCH] HBASE-2755 Duplicate assignment of a region after region
 server recovery

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@980649 13f79535-47bb-0310-9956-ffa450edef68
---
 CHANGES.txt                                   |  2 ++
 .../hadoop/hbase/master/BaseScanner.java      | 36 ++++++++++++++-----
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index e21f620c68a..e8475f7aff2 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -461,6 +461,8 @@ Release 0.21.0 - Unreleased
    HBASE-2884  TestHFileOutputFormat flaky when map tasks generate identical
                data
    HBASE-2890  Initialize RPC JMX metrics on startup (Gary Helmling via Stack)
+   HBASE-2755  Duplicate assignment of a region after region server recovery
+               (Kannan Muthukkaruppan via Stack)
 
   IMPROVEMENTS
    HBASE-1760  Cleanup TODOs in HTable
diff --git a/src/main/java/org/apache/hadoop/hbase/master/BaseScanner.java b/src/main/java/org/apache/hadoop/hbase/master/BaseScanner.java
index 29abe356438..69eab39aa3d 100644
--- a/src/main/java/org/apache/hadoop/hbase/master/BaseScanner.java
+++ b/src/main/java/org/apache/hadoop/hbase/master/BaseScanner.java
@@ -194,7 +194,7 @@ abstract class BaseScanner extends Chore {
         long startCode = getStartCode(values);
 
         // Note Region has been assigned.
-        checkAssigned(regionServer, region, info, serverAddress, startCode);
+        checkAssigned(regionServer, region, info, serverAddress, startCode, true);
         if (isSplitParent(info)) {
           splitParents.put(info, values);
         }
@@ -533,12 +533,15 @@ abstract class BaseScanner extends Chore {
    * @param info
    * @param hostnameAndPort hostname ':' port as it comes out of .META.
    * @param startCode
+   * @param checkTwice should we check twice before adding a region
+   * to unassigned pool.              
    * @throws IOException
    */
   protected void checkAssigned(final HRegionInterface regionServer,
     final MetaRegion meta, final HRegionInfo info,
-    final String hostnameAndPort, final long startCode)
+    final String hostnameAndPort, final long startCode, boolean checkTwice)
   throws IOException {
+    boolean tryAgain = false;
     String serverName = null;
     String sa = hostnameAndPort;
     long sc = startCode;
@@ -575,16 +578,31 @@ abstract class BaseScanner extends Chore {
       // If we can't find the HServerInfo, then add it to the list of
       //  unassigned regions.
       if (storedInfo == null) {
-        // The current assignment is invalid
-        if (LOG.isDebugEnabled()) {
-          LOG.debug("Current assignment of " + info.getRegionNameAsString() +
-            " is not valid; " + " serverAddress=" + sa +
-            ", startCode=" + sc + " unknown.");
+        if (checkTwice) {
+          tryAgain = true;
+        } else {
+          if (LOG.isDebugEnabled()) {
+            LOG.debug("Current assignment of " + info.getRegionNameAsString() +
+              " is not valid; " + " serverAddress=" + sa +
+              ", startCode=" + sc + " unknown.");
+          }
+          // Now get the region assigned
+          this.master.getRegionManager().setUnassigned(info, true);
         }
-        // Now get the region assigned
-        this.master.getRegionManager().setUnassigned(info, true);
       }
     }
+    if (tryAgain) {
+      // The current assignment is invalid. But we need to try again.
+      if (LOG.isDebugEnabled()) {
+        LOG.debug("Current assignment of " + info.getRegionNameAsString() +
+          " is not valid; " + " serverAddress=" + sa +
+          ", startCode=" + sc + " unknown; checking once more!");
+      }
+      // passing null for hostNameAndPort will force the function
+      // to reget the assignment from META and protect against
+      // double assignment race conditions (HBASE-2755).
+      checkAssigned(regionServer, meta, info, null, 0, false);
+    }
   }
 
   /**