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Server functionality for HBase
/*
*
* 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 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 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
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
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 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 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 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 ctx, TableName tableName)
throws IOException;
/**
* Called before {@link org.apache.hadoop.hbase.master.HMaster} truncates a
* table. Called as part of truncate 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 preTruncateTable(final ObserverContext ctx,
TableName tableName) throws IOException;
/**
* Called after the truncateTable operation has been requested. Called as part
* of truncate table RPC call.
* The truncate is synchronous, so this method will be called when the
* truncate operation is terminated.
* @param ctx the environment to interact with the framework and master
* @param tableName the name of the table
*/
void postTruncateTable(final ObserverContext ctx,
TableName tableName) throws IOException;
/**
* Called before {@link org.apache.hadoop.hbase.master.HMaster} truncates a
* table. Called as part of truncate table handler and it is sync
* to the truncate 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 preTruncateTableHandler(
final ObserverContext ctx, TableName tableName)
throws IOException;
/**
* Called after {@link org.apache.hadoop.hbase.master.HMaster} truncates a
* table. Called as part of truncate table handler and it is sync to the
* truncate 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 postTruncateTableHandler(
final ObserverContext 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 ctx,
final HRegionInfo regionInfo, final boolean force) throws IOException;
/**
* Called prior to marking a given region as offline. ctx.bypass() 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 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 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 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 ctx, List 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 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 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 ctx)
throws IOException;
/**
* Called immediately prior to stopping this
* {@link org.apache.hadoop.hbase.master.HMaster} process.
*/
void preStopMaster(final ObserverContext 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 ctx)
throws IOException;
/**
* Call before the master initialization is set to true.
* {@link org.apache.hadoop.hbase.master.HMaster} process.
*/
void preMasterInitialization(final ObserverContext 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 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 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 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 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 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 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 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 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 ctx,
List tableNamesList,
List 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 ctx,
List 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 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 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 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 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 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 ctx,
NamespaceDescriptor ns) throws IOException;
/**
* Called before a getNamespaceDescriptor request has been processed.
* @param ctx the environment to interact with the framework and master
* @param namespace the name of the namespace
* @throws IOException
*/
void preGetNamespaceDescriptor(ObserverContext ctx,
String namespace) throws IOException;
/**
* Called after a getNamespaceDescriptor request has been processed.
* @param ctx the environment to interact with the framework and master
* @param ns the NamespaceDescriptor
* @throws IOException
*/
void postGetNamespaceDescriptor(ObserverContext ctx,
NamespaceDescriptor ns) throws IOException;
/**
* Called before a listNamespaceDescriptors request has been processed.
* @param ctx the environment to interact with the framework and master
* @param descriptors an empty list, can be filled with what to return if bypassing
* @throws IOException
*/
void preListNamespaceDescriptors(ObserverContext ctx,
List descriptors) throws IOException;
/**
* Called after a listNamespaceDescriptors 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 postListNamespaceDescriptors(ObserverContext ctx,
List descriptors) throws IOException;
}