HBASE-4815 Disable online altering by default, create a config for it

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1203916 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -437,6 +437,7 @@ Release 0.92.0 - Unreleased
    HBASE-4796  Race between SplitRegionHandlers for the same region kills the master
    HBASE-4816  Regionserver wouldn't go down because split happened exactly at same
                time we issued bulk user region close call on our way out
+   HBASE-4815  Disable online altering by default, create a config for it
 
   TESTS
    HBASE-4450  test for number of blocks read: to serve as baseline for expected

src/main/java/org/apache/hadoop/hbase/master/handler/TableEventHandler.java

@@ -69,7 +69,8 @@ public abstract class TableEventHandler extends EventHandler {
     try {
       this.masterServices.checkTableModifiable(tableName);
     } catch (TableNotDisabledException ex)  {
-      if (eventType.isOnlineSchemaChangeSupported()) {
+      if (isOnlineSchemaChangeAllowed()
+          && eventType.isOnlineSchemaChangeSupported()) {
         LOG.debug("Ignoring table not disabled exception " +
             "for supporting online schema changes.");
       }	else {
@@ -79,6 +80,11 @@ public abstract class TableEventHandler extends EventHandler {
     this.tableNameStr = Bytes.toString(this.tableName);
   }
 
+  private boolean isOnlineSchemaChangeAllowed() {
+    return this.server.getConfiguration().getBoolean(
+        "hbase.online.schema.update.enable", false);
+  }
+
   @Override
   public void process() {
     try {

src/main/resources/hbase-default.xml

@@ -781,6 +781,16 @@
       simplify coprocessor failure analysis.
       </description>
   </property>
+  <property>
+    <name>hbase.online.schema.update.enable</name>
+    <value>false</value>
+    <description>
+    Set true to enable online schema changes.  This is an experimental feature.  
+    There are known issues modifying table schemas at the same time a region
+    split is happening so your table needs to be quiescent or else you have to
+    be running with splits disabled.
+    </description>
+  </property>
   <property>
     <name>dfs.support.append</name>
     <value>true</value>

src/test/java/org/apache/hadoop/hbase/client/TestAdmin.java

@@ -308,6 +308,8 @@ public class TestAdmin {
   @Test 
   public void testOnlineChangeTableSchema() throws IOException, InterruptedException {
     final byte [] tableName = Bytes.toBytes("changeTableSchemaOnline");
+    TEST_UTIL.getMiniHBaseCluster().getMaster().getConfiguration().setBoolean(
+        "hbase.online.schema.update.enable", true);
     HTableDescriptor [] tables = admin.listTables();
     int numTables = tables.length;
     TEST_UTIL.createTable(tableName, HConstants.CATALOG_FAMILY);
@@ -390,6 +392,38 @@ public class TestAdmin {
     assertFalse(this.admin.tableExists(tableName));
   }
   
+  @Test
+  public void testShouldFailOnlineSchemaUpdateIfOnlineSchemaIsNotEnabled()
+      throws Exception {
+    final byte[] tableName = Bytes.toBytes("changeTableSchemaOnlineFailure");
+    TEST_UTIL.getMiniHBaseCluster().getMaster().getConfiguration().setBoolean(
+        "hbase.online.schema.update.enable", false);
+    HTableDescriptor[] tables = admin.listTables();
+    int numTables = tables.length;
+    TEST_UTIL.createTable(tableName, HConstants.CATALOG_FAMILY);
+    tables = this.admin.listTables();
+    assertEquals(numTables + 1, tables.length);
+
+    // FIRST, do htabledescriptor changes.
+    HTableDescriptor htd = this.admin.getTableDescriptor(tableName);
+    // Make a copy and assert copy is good.
+    HTableDescriptor copy = new HTableDescriptor(htd);
+    assertTrue(htd.equals(copy));
+    // Now amend the copy. Introduce differences.
+    long newFlushSize = htd.getMemStoreFlushSize() / 2;
+    copy.setMemStoreFlushSize(newFlushSize);
+    final String key = "anyoldkey";
+    assertTrue(htd.getValue(key) == null);
+    copy.setValue(key, key);
+    boolean expectedException = false;
+    try {
+      modifyTable(tableName, copy);
+    } catch (TableNotDisabledException re) {
+      expectedException = true;
+    }
+    assertTrue("Online schema update should not happen.", expectedException);
+  }
+
   /**
    * Modify table is async so wait on completion of the table operation in master.
    * @param tableName