/*
    *
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.hadoop.hbase.coprocessor;
  
  import java.io.IOException;
  import java.util.List;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.Coprocessor;
  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.HColumnDescriptor;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.NamespaceDescriptor;
  import org.apache.hadoop.hbase.ServerName;
  import org.apache.hadoop.hbase.master.RegionPlan;
  import org.apache.hadoop.hbase.protobuf.generated.HBaseProtos.SnapshotDescription;
  
  /**
   * Defines coprocessor hooks for interacting with operations on the
   * {@link org.apache.hadoop.hbase.master.HMaster} process.
   */
  @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
  @InterfaceStability.Evolving
  public interface MasterObserver extends Coprocessor {
  
    /**
     * Called before a new table is created by
     * {@link org.apache.hadoop.hbase.master.HMaster}.  Called as part of create
     * table RPC call.
     * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
     * @param ctx the environment to interact with the framework and master
     * @param desc the HTableDescriptor for the table
     * @param regions the initial regions created for the table
     * @throws IOException
     */
    void preCreateTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
        HTableDescriptor desc, HRegionInfo[] regions) throws IOException;
  
    /**
     * Called after the createTable operation has been requested.  Called as part
     * of create table RPC call.
     * @param ctx the environment to interact with the framework and master
     * @param desc the HTableDescriptor for the table
     * @param regions the initial regions created for the table
     * @throws IOException
     */
    void postCreateTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
        HTableDescriptor desc, HRegionInfo[] regions) throws IOException;
    /**
     * Called before a new table is created by
     * {@link org.apache.hadoop.hbase.master.HMaster}.  Called as part of create
     * table handler and it is async to the create RPC call.
     * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
     * @param ctx the environment to interact with the framework and master
     * @param desc the HTableDescriptor for the table
     * @param regions the initial regions created for the table
     * @throws IOException
     */
    void preCreateTableHandler(final ObserverContext<MasterCoprocessorEnvironment>
        ctx, HTableDescriptor desc, HRegionInfo[] regions) throws IOException;
  
    /**
     * Called after the createTable operation has been requested.  Called as part
     * of create table RPC call.  Called as part of create table handler and
     * it is async to the create RPC call.
     * @param ctx the environment to interact with the framework and master
     * @param desc the HTableDescriptor for the table
     * @param regions the initial regions created for the table
     * @throws IOException
     */
    void postCreateTableHandler(final ObserverContext<MasterCoprocessorEnvironment>
    ctx, HTableDescriptor desc, HRegionInfo[] regions) throws IOException;
  
    /**
     * Called before {@link org.apache.hadoop.hbase.master.HMaster} deletes a
     * table.  Called as part of delete table RPC call.
     * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
     * @param ctx the environment to interact with the framework and master
     * @param tableName the name of the table
    */
   void preDeleteTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName) throws IOException;
 
   /**
    * Called after the deleteTable operation has been requested.  Called as part
    * of delete table RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void postDeleteTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName) throws IOException;
 
   /**
    * Called before {@link org.apache.hadoop.hbase.master.HMaster} deletes a
    * table.  Called as part of delete table handler and
    * it is async to the delete RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void preDeleteTableHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx, TableName tableName)
       throws IOException;
 
   /**
    * Called after {@link org.apache.hadoop.hbase.master.HMaster} deletes a
    * table.  Called as part of delete table handler and it is async to the
    * delete RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void postDeleteTableHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx, TableName tableName)
       throws IOException;
 
   /**
    * Called prior to modifying a table's properties.  Called as part of modify
    * table RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param htd the HTableDescriptor
    */
   void preModifyTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName, HTableDescriptor htd) throws IOException;
 
   /**
    * Called after the modifyTable operation has been requested.  Called as part
    * of modify table RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param htd the HTableDescriptor
    */
   void postModifyTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName, HTableDescriptor htd) throws IOException;
 
   /**
    * Called prior to modifying a table's properties.  Called as part of modify
    * table handler and it is async to the modify table RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param htd the HTableDescriptor
    */
   void preModifyTableHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName, HTableDescriptor htd) throws IOException;
 
   /**
    * Called after to modifying a table's properties.  Called as part of modify
    * table handler and it is async to the modify table RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param htd the HTableDescriptor
    */
   void postModifyTableHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName, HTableDescriptor htd) throws IOException;
 
   /**
    * Called prior to adding a new column family to the table.  Called as part of
    * add column RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param column the HColumnDescriptor
    */
   void preAddColumn(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName, HColumnDescriptor column) throws IOException;
 
   /**
    * Called after the new column family has been created.  Called as part of
    * add column RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param column the HColumnDescriptor
    */
   void postAddColumn(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName, HColumnDescriptor column) throws IOException;
 
   /**
    * Called prior to adding a new column family to the table.  Called as part of
    * add column handler.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param column the HColumnDescriptor
    */
   void preAddColumnHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName, HColumnDescriptor column) throws IOException;
 
   /**
    * Called after the new column family has been created.  Called as part of
    * add column handler.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param column the HColumnDescriptor
    */
   void postAddColumnHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName, HColumnDescriptor column) throws IOException;
 
   /**
    * Called prior to modifying a column family's attributes.  Called as part of
    * modify column RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param descriptor the HColumnDescriptor
    */
   void preModifyColumn(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName, HColumnDescriptor descriptor) throws IOException;
 
   /**
    * Called after the column family has been updated.  Called as part of modify
    * column RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param descriptor the HColumnDescriptor
    */
   void postModifyColumn(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName, HColumnDescriptor descriptor) throws IOException;
 
   /**
    * Called prior to modifying a column family's attributes.  Called as part of
    * modify column handler.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param descriptor the HColumnDescriptor
    */
   void preModifyColumnHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName, HColumnDescriptor descriptor) throws IOException;
 
   /**
    * Called after the column family has been updated.  Called as part of modify
    * column handler.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param descriptor the HColumnDescriptor
    */
   void postModifyColumnHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       TableName tableName, HColumnDescriptor descriptor) throws IOException;
 
 
   /**
    * Called prior to deleting the entire column family.  Called as part of
    * delete column RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param c the column
    */
   void preDeleteColumn(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName, final byte[] c) throws IOException;
 
   /**
    * Called after the column family has been deleted.  Called as part of delete
    * column RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param c the column
    */
   void postDeleteColumn(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName, final byte[] c) throws IOException;
 
   /**
    * Called prior to deleting the entire column family.  Called as part of
    * delete column handler.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param c the column
    */
   void preDeleteColumnHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName, final byte[] c) throws IOException;
 
   /**
    * Called after the column family has been deleted.  Called as part of
    * delete column handler.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    * @param c the column
    */
   void postDeleteColumnHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName, final byte[] c) throws IOException;
 
   /**
    * Called prior to enabling a table.  Called as part of enable table RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void preEnableTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName) throws IOException;
 
   /**
    * Called after the enableTable operation has been requested.  Called as part
    * of enable table RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void postEnableTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName) throws IOException;
 
   /**
    * Called prior to enabling a table.  Called as part of enable table handler
    * and it is async to the enable table RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void preEnableTableHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName) throws IOException;
 
   /**
    * Called after the enableTable operation has been requested.  Called as part
    * of enable table handler and it is async to the enable table RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void postEnableTableHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName) throws IOException;
 
   /**
    * Called prior to disabling a table.  Called as part of disable table RPC
    * call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void preDisableTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName) throws IOException;
 
   /**
    * Called after the disableTable operation has been requested.  Called as part
    * of disable table RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void postDisableTable(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName) throws IOException;
 
   /**
    * Called prior to disabling a table.  Called as part of disable table handler
    * and it is asyn to the disable table RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void preDisableTableHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName) throws IOException;
 
   /**
    * Called after the disableTable operation has been requested.  Called as part
    * of disable table handler and it is asyn to the disable table RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param tableName the name of the table
    */
   void postDisableTableHandler(
       final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final TableName tableName) throws IOException;
 
   /**
    * Called prior to moving a given region from one region server to another.
    * @param ctx the environment to interact with the framework and master
    * @param region the HRegionInfo
    * @param srcServer the source ServerName
    * @param destServer the destination ServerName
    */
   void preMove(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final HRegionInfo region, final ServerName srcServer,
       final ServerName destServer)
     throws IOException;
 
   /**
    * Called after the region move has been requested.
    * @param ctx the environment to interact with the framework and master
    * @param region the HRegionInfo
    * @param srcServer the source ServerName
    * @param destServer the destination ServerName
    */
   void postMove(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final HRegionInfo region, final ServerName srcServer,
       final ServerName destServer)
     throws IOException;
 
   /**
    * Called prior to assigning a specific region.
    * @param ctx the environment to interact with the framework and master
    * @param regionInfo the regionInfo of the region
    */
   void preAssign(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final HRegionInfo regionInfo) throws IOException;
 
   /**
    * Called after the region assignment has been requested.
    * @param ctx the environment to interact with the framework and master
    * @param regionInfo the regionInfo of the region
    */
   void postAssign(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final HRegionInfo regionInfo) throws IOException;
 
   /**
    * Called prior to unassigning a given region.
    * @param ctx the environment to interact with the framework and master
    * @param regionInfo
    * @param force whether to force unassignment or not
    */
   void preUnassign(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final HRegionInfo regionInfo, final boolean force) throws IOException;
 
   /**
    * Called after the region unassignment has been requested.
    * @param ctx the environment to interact with the framework and master
    * @param regionInfo
    * @param force whether to force unassignment or not
    */
   void postUnassign(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final HRegionInfo regionInfo, final boolean force) throws IOException;
 
   /**
    * Called prior to marking a given region as offline. <code>ctx.bypass()</code> will not have any
    * impact on this hook.
    * @param ctx the environment to interact with the framework and master
    * @param regionInfo
    */
   void preRegionOffline(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final HRegionInfo regionInfo) throws IOException;
 
   /**
    * Called after the region has been marked offline.
    * @param ctx the environment to interact with the framework and master
    * @param regionInfo
    */
   void postRegionOffline(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final HRegionInfo regionInfo) throws IOException;
 
   /**
    * Called prior to requesting rebalancing of the cluster regions, though after
    * the initial checks for regions in transition and the balance switch flag.
    * @param ctx the environment to interact with the framework and master
    */
   void preBalance(final ObserverContext<MasterCoprocessorEnvironment> ctx)
       throws IOException;
 
   /**
    * Called after the balancing plan has been submitted.
    * @param ctx the environment to interact with the framework and master
    * @param plans the RegionPlans which master has executed. RegionPlan serves as hint
    * as for the final destination for the underlying region but may not represent the
    * final state of assignment
    */
   void postBalance(final ObserverContext<MasterCoprocessorEnvironment> ctx, List<RegionPlan> plans)
       throws IOException;
 
   /**
    * Called prior to modifying the flag used to enable/disable region balancing.
    * @param ctx the coprocessor instance's environment
    * @param newValue the new flag value submitted in the call
    */
   boolean preBalanceSwitch(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final boolean newValue) throws IOException;
 
   /**
    * Called after the flag to enable/disable balancing has changed.
    * @param ctx the coprocessor instance's environment
    * @param oldValue the previously set balanceSwitch value
    * @param newValue the newly set balanceSwitch value
    */
   void postBalanceSwitch(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final boolean oldValue, final boolean newValue) throws IOException;
 
   /**
    * Called prior to shutting down the full HBase cluster, including this
    * {@link org.apache.hadoop.hbase.master.HMaster} process.
    */
   void preShutdown(final ObserverContext<MasterCoprocessorEnvironment> ctx)
       throws IOException;
 
 
   /**
    * Called immediately prior to stopping this
    * {@link org.apache.hadoop.hbase.master.HMaster} process.
    */
   void preStopMaster(final ObserverContext<MasterCoprocessorEnvironment> ctx)
       throws IOException;
 
   /**
    * Called immediately after an active master instance has completed
    * initialization.  Will not be called on standby master instances unless
    * they take over the active role.
    */
   void postStartMaster(final ObserverContext<MasterCoprocessorEnvironment> ctx)
       throws IOException;
 
   /**
    * Call before the master initialization is set to true.
    * {@link org.apache.hadoop.hbase.master.HMaster} process.
    */
   void preMasterInitialization(final ObserverContext<MasterCoprocessorEnvironment> ctx)
       throws IOException;
 
   /**
    * Called before a new snapshot is taken.
    * Called as part of snapshot RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param snapshot the SnapshotDescriptor for the snapshot
    * @param hTableDescriptor the hTableDescriptor of the table to snapshot
    * @throws IOException
    */
   void preSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final SnapshotDescription snapshot, final HTableDescriptor hTableDescriptor)
       throws IOException;
 
   /**
    * Called after the snapshot operation has been requested.
    * Called as part of snapshot RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param snapshot the SnapshotDescriptor for the snapshot
    * @param hTableDescriptor the hTableDescriptor of the table to snapshot
    * @throws IOException
    */
   void postSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final SnapshotDescription snapshot, final HTableDescriptor hTableDescriptor)
       throws IOException;
 
   /**
    * Called before a snapshot is cloned.
    * Called as part of restoreSnapshot RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param snapshot the SnapshotDescriptor for the snapshot
    * @param hTableDescriptor the hTableDescriptor of the table to create
    * @throws IOException
    */
   void preCloneSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final SnapshotDescription snapshot, final HTableDescriptor hTableDescriptor)
       throws IOException;
 
   /**
    * Called after a snapshot clone operation has been requested.
    * Called as part of restoreSnapshot RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param snapshot the SnapshotDescriptor for the snapshot
    * @param hTableDescriptor the hTableDescriptor of the table to create
    * @throws IOException
    */
   void postCloneSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final SnapshotDescription snapshot, final HTableDescriptor hTableDescriptor)
       throws IOException;
 
   /**
    * Called before a snapshot is restored.
    * Called as part of restoreSnapshot RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param snapshot the SnapshotDescriptor for the snapshot
    * @param hTableDescriptor the hTableDescriptor of the table to restore
    * @throws IOException
    */
   void preRestoreSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final SnapshotDescription snapshot, final HTableDescriptor hTableDescriptor)
       throws IOException;
 
   /**
    * Called after a snapshot restore operation has been requested.
    * Called as part of restoreSnapshot RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param snapshot the SnapshotDescriptor for the snapshot
    * @param hTableDescriptor the hTableDescriptor of the table to restore
    * @throws IOException
    */
   void postRestoreSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final SnapshotDescription snapshot, final HTableDescriptor hTableDescriptor)
       throws IOException;
 
   /**
    * Called before a snapshot is deleted.
    * Called as part of deleteSnapshot RPC call.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param snapshot the SnapshotDescriptor of the snapshot to delete
    * @throws IOException
    */
   void preDeleteSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final SnapshotDescription snapshot) throws IOException;
 
   /**
    * Called after the delete snapshot operation has been requested.
    * Called as part of deleteSnapshot RPC call.
    * @param ctx the environment to interact with the framework and master
    * @param snapshot the SnapshotDescriptor of the snapshot to delete
    * @throws IOException
    */
   void postDeleteSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       final SnapshotDescription snapshot) throws IOException;
 
   /**
    * Called before a getTableDescriptors request has been processed.
    * @param ctx the environment to interact with the framework and master
    * @param tableNamesList the list of table names, or null if querying for all
    * @param descriptors an empty list, can be filled with what to return if bypassing
    * @throws IOException
    */
   void preGetTableDescriptors(ObserverContext<MasterCoprocessorEnvironment> ctx,
       List<TableName> tableNamesList,
       List<HTableDescriptor> descriptors) throws IOException;
 
   /**
    * Called after a getTableDescriptors request has been processed.
    * @param ctx the environment to interact with the framework and master
    * @param descriptors the list of descriptors about to be returned
    * @throws IOException
    */
   void postGetTableDescriptors(ObserverContext<MasterCoprocessorEnvironment> ctx,
       List<HTableDescriptor> descriptors) throws IOException;
 
   /**
    * Called before a new namespace is created by
    * {@link org.apache.hadoop.hbase.master.HMaster}.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param ns the NamespaceDescriptor for the table
    * @throws IOException
    */
   void preCreateNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       NamespaceDescriptor ns) throws IOException;
   /**
    * Called after the createNamespace operation has been requested.
    * @param ctx the environment to interact with the framework and master
    * @param ns the NamespaceDescriptor for the table
    * @throws IOException
    */
   void postCreateNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
        NamespaceDescriptor ns) throws IOException;
 
   /**
    * Called before {@link org.apache.hadoop.hbase.master.HMaster} deletes a
    * namespace
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param namespace the name of the namespace
    */
   void preDeleteNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       String namespace) throws IOException;
 
   /**
    * Called after the deleteNamespace operation has been requested.
    * @param ctx the environment to interact with the framework and master
    * @param namespace the name of the namespace
    */
   void postDeleteNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       String namespace) throws IOException;
 
   /**
    * Called prior to modifying a namespace's properties.
    * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
    * @param ctx the environment to interact with the framework and master
    * @param ns the NamespaceDescriptor
    */
   void preModifyNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       NamespaceDescriptor ns) throws IOException;
 
   /**
    * Called after the modifyNamespace operation has been requested.
    * @param ctx the environment to interact with the framework and master
    * @param ns the NamespaceDescriptor
    */
   void postModifyNamespace(final ObserverContext<MasterCoprocessorEnvironment> ctx,
       NamespaceDescriptor ns) throws IOException;
 }