Package org.apache.hadoop.hbase

Class MetaRegionLocationCache

java.lang.Object

org.apache.hadoop.hbase.zookeeper.ZKListener

org.apache.hadoop.hbase.MetaRegionLocationCache

@Private
public class MetaRegionLocationCache
extends ZKListener

A cache of meta region location metadata. Registers a listener on ZK to track changes to the meta table znodes. Clients are expected to retry if the meta information is stale. This class is thread-safe (a single instance of this class can be shared by multiple threads without race conditions).

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static enum	MetaRegionLocationCache.ZNodeOpType

Field Summary

Fields

Modifier and Type	Field	Description
private final CopyOnWriteArrayMap<Integer,HRegionLocation>	cachedMetaLocations	Cached meta region locations indexed by replica ID.
private static final org.slf4j.Logger	LOG
private static final int	MAX_ZK_META_FETCH_RETRIES	Maximum number of times we retry when ZK operation times out.
private final RetryCounterFactory	retryCounterFactory
private static final int	SLEEP_INTERVAL_MS_BETWEEN_RETRIES	Sleep interval ms between ZK operation retries.
private static final int	SLEEP_INTERVAL_MS_MAX

Fields inherited from class org.apache.hadoop.hbase.zookeeper.ZKListener

watcher

Constructor Summary

Constructors

Constructor	Description
MetaRegionLocationCache(ZKWatcher zkWatcher)

Method Summary

Modifier and Type	Method	Description
private HRegionLocation	getMetaRegionLocation(int replicaId)	Gets the HRegionLocation for a given meta replica ID.
List<HRegionLocation>	getMetaRegionLocations()	Returns Optional list of HRegionLocations for meta replica(s), null if the cache is empty.
private boolean	isValidMetaPath(String path)	Helper to check if the given 'path' corresponds to a meta znode.
private void	loadMetaLocationsFromZk(RetryCounter retryCounter, MetaRegionLocationCache.ZNodeOpType opType)	Populates the current snapshot of meta locations from ZK.
void	nodeChildrenChanged(String path)	Called when an existing node has a child node added or removed.
void	nodeCreated(String path)	Called when a new node has been created.
void	nodeDataChanged(String path)	Called when an existing node has changed data.
void	nodeDeleted(String path)	Called when a node has been deleted
private void	updateMetaLocation(String path, MetaRegionLocationCache.ZNodeOpType opType)

Methods inherited from class org.apache.hadoop.hbase.zookeeper.ZKListener

getWatcher

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

LOG

private static final org.slf4j.Logger LOG

MAX_ZK_META_FETCH_RETRIES

private static final int MAX_ZK_META_FETCH_RETRIES

Maximum number of times we retry when ZK operation times out.

See Also:

• Constant Field Values

SLEEP_INTERVAL_MS_BETWEEN_RETRIES

private static final int SLEEP_INTERVAL_MS_BETWEEN_RETRIES

Sleep interval ms between ZK operation retries.

See Also:

• Constant Field Values

SLEEP_INTERVAL_MS_MAX

private static final int SLEEP_INTERVAL_MS_MAX

See Also:

• Constant Field Values

retryCounterFactory

private final RetryCounterFactory retryCounterFactory

cachedMetaLocations

private final CopyOnWriteArrayMap<Integer,HRegionLocation> cachedMetaLocations

Cached meta region locations indexed by replica ID. CopyOnWriteArrayMap ensures synchronization during updates and a consistent snapshot during client requests. Even though CopyOnWriteArrayMap copies the data structure for every write, that should be OK since the size of the list is often small and mutations are not too often and we do not need to block client requests while mutations are in progress.

Constructor Details

MetaRegionLocationCache

public MetaRegionLocationCache(ZKWatcher zkWatcher)

Method Details

loadMetaLocationsFromZk

private void loadMetaLocationsFromZk(RetryCounter retryCounter,
 MetaRegionLocationCache.ZNodeOpType opType)

Populates the current snapshot of meta locations from ZK. If no meta znodes exist, it registers a watcher on base znode to check for any CREATE/DELETE events on the children.

Parameters:

retryCounter - controls the number of retries and sleep between retries.

getMetaRegionLocation

private HRegionLocation getMetaRegionLocation(int replicaId)
                                       throws org.apache.zookeeper.KeeperException

Gets the HRegionLocation for a given meta replica ID. Renews the watch on the znode for future updates.

Parameters:

replicaId - ReplicaID of the region.

Returns:

HRegionLocation for the meta replica.

Throws:

org.apache.zookeeper.KeeperException - if there is any issue fetching/parsing the serialized data.

updateMetaLocation

private void updateMetaLocation(String path,
 MetaRegionLocationCache.ZNodeOpType opType)

getMetaRegionLocations

public List<HRegionLocation> getMetaRegionLocations()

Returns Optional list of HRegionLocations for meta replica(s), null if the cache is empty.

isValidMetaPath

private boolean isValidMetaPath(String path)

Helper to check if the given 'path' corresponds to a meta znode. This listener is only interested in changes to meta znodes.

nodeCreated

public void nodeCreated(String path)

Description copied from class: ZKListener

Called when a new node has been created.

Overrides:

nodeCreated in class ZKListener

Parameters:

path - full path of the new node

nodeDeleted

public void nodeDeleted(String path)

Description copied from class: ZKListener

Called when a node has been deleted

Overrides:

nodeDeleted in class ZKListener

Parameters:

path - full path of the deleted node

nodeDataChanged

public void nodeDataChanged(String path)

Description copied from class: ZKListener

Called when an existing node has changed data.

Overrides:

nodeDataChanged in class ZKListener

Parameters:

path - full path of the updated node

nodeChildrenChanged

public void nodeChildrenChanged(String path)

Description copied from class: ZKListener

Called when an existing node has a child node added or removed.

Overrides:

nodeChildrenChanged in class ZKListener

Parameters:

path - full path of the node whose children have changed