Package org.apache.hadoop.hbase.client

Class CatalogReplicaLoadBalanceSimpleSelector

java.lang.Object

org.apache.hadoop.hbase.client.CatalogReplicaLoadBalanceSimpleSelector

All Implemented Interfaces:

CatalogReplicaLoadBalanceSelector, Stoppable

class CatalogReplicaLoadBalanceSimpleSelector
extends Object
implements CatalogReplicaLoadBalanceSelector, Stoppable

CatalogReplicaLoadBalanceReplicaSimpleSelector implements a simple catalog replica load balancing algorithm. It maintains a stale location cache for each table. Whenever client looks up location, it first check if the row is the stale location cache. If yes, the location from catalog replica is stale, it will go to the primary region to look up update-to-date location; otherwise, it will randomly pick up a replica region or primary region for lookup. When clients receive RegionNotServedException from region servers, it will add these region locations to the stale location cache. The stale cache will be cleaned up periodically by a chore.

It follows a simple algorithm to choose a meta replica region (including primary meta) to go:

1. If there is no stale location entry for rows it looks up, it will randomly pick a meta replica region (including primary meta) to do lookup.
2. If the location from the replica region is stale, client gets RegionNotServedException from region server, in this case, it will create StaleLocationCacheEntry in CatalogReplicaLoadBalanceReplicaSimpleSelector.
3. When client tries to do location lookup, it checks StaleLocationCache first for rows it tries to lookup, if entry exists, it will go with primary meta region to do lookup; otherwise, it will follow step 1.
4. A chore will periodically run to clean up cache entries in the StaleLocationCache.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static final class	CatalogReplicaLoadBalanceSimpleSelector.StaleLocationCacheEntry	StaleLocationCacheEntry is the entry when a stale location is reported by an client.

Field Summary

Fields

Modifier and Type	Field	Description
private final ChoreService	choreService
private final IntSupplier	getNumOfReplicas
private boolean	isStopped
private static final org.slf4j.Logger	LOG
private int	numOfReplicas
private final int	REFRESH_REPLICA_COUNT_CHORE_INTERVAL_IN_MILLISECONDS
private final int	STALE_CACHE_CLEAN_CHORE_INTERVAL_IN_MILLISECONDS
private final long	STALE_CACHE_TIMEOUT_IN_MILLISECONDS
private final ConcurrentMap<TableName,ConcurrentNavigableMap<byte[],CatalogReplicaLoadBalanceSimpleSelector.StaleLocationCacheEntry>>	staleCache
private final TableName	tableName

Fields inherited from interface org.apache.hadoop.hbase.client.CatalogReplicaLoadBalanceSelector

UNINITIALIZED_NUM_OF_REPLICAS

Constructor Summary

Constructors

Constructor	Description
CatalogReplicaLoadBalanceSimpleSelector(TableName tableName, ChoreService choreService, IntSupplier getNumOfReplicas)

Method Summary

Modifier and Type	Method	Description
private void	cleanupReplicaReplicaStaleCache()
private ScheduledChore	getCacheCleanupChore(CatalogReplicaLoadBalanceSimpleSelector selector)
private int	getRandomReplicaId()	Select an random replica id (including the primary replica id).
private ScheduledChore	getRefreshReplicaCountChore(CatalogReplicaLoadBalanceSimpleSelector selector)
boolean	isStopped()	Returns True if Stoppable.stop(String) has been closed.
void	onError(HRegionLocation loc)	When a client runs into RegionNotServingException, it will call this method to update Selector's internal state.
private int	refreshCatalogReplicaCount()
int	select(TableName tableName, byte[] row, RegionLocateType locateType)	When it looks up a location, it will call this method to find a replica region to go.
void	stop(String why)	Stop this service.

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

STALE_CACHE_TIMEOUT_IN_MILLISECONDS

private final long STALE_CACHE_TIMEOUT_IN_MILLISECONDS

See Also:

• Constant Field Values

STALE_CACHE_CLEAN_CHORE_INTERVAL_IN_MILLISECONDS

private final int STALE_CACHE_CLEAN_CHORE_INTERVAL_IN_MILLISECONDS

See Also:

• Constant Field Values

REFRESH_REPLICA_COUNT_CHORE_INTERVAL_IN_MILLISECONDS

private final int REFRESH_REPLICA_COUNT_CHORE_INTERVAL_IN_MILLISECONDS

See Also:

• Constant Field Values

staleCache

private final ConcurrentMap<TableName,ConcurrentNavigableMap<byte[],CatalogReplicaLoadBalanceSimpleSelector.StaleLocationCacheEntry>> staleCache

numOfReplicas

private volatile int numOfReplicas

choreService

private final ChoreService choreService

tableName

private final TableName tableName

getNumOfReplicas

private final IntSupplier getNumOfReplicas

isStopped

private volatile boolean isStopped

Constructor Details

CatalogReplicaLoadBalanceSimpleSelector

CatalogReplicaLoadBalanceSimpleSelector(TableName tableName,
 ChoreService choreService,
 IntSupplier getNumOfReplicas)

Method Details

onError

public void onError(HRegionLocation loc)

When a client runs into RegionNotServingException, it will call this method to update Selector's internal state.

Specified by:

onError in interface CatalogReplicaLoadBalanceSelector

Parameters:

loc - the location which causes exception.

getRandomReplicaId

private int getRandomReplicaId()

Select an random replica id (including the primary replica id). In case there is no replica region configured, return the primary replica id.

Returns:

Replica id

select

public int select(TableName tableName,
 byte[] row,
 RegionLocateType locateType)

When it looks up a location, it will call this method to find a replica region to go. For a normal case, > 99% of region locations from catalog/meta replica will be up to date. In extreme cases such as region server crashes, it will depends on how fast replication catches up.

Specified by:

select in interface CatalogReplicaLoadBalanceSelector

Parameters:

tableName - table name it looks up

row - key it looks up.

locateType - locateType, Only BEFORE and CURRENT will be passed in.

Returns:

catalog replica id

stop

public void stop(String why)

Description copied from interface: Stoppable

Stop this service. Implementers should favor logging errors over throwing RuntimeExceptions.

Specified by:

stop in interface Stoppable

Parameters:

why - Why we're stopping.

isStopped

public boolean isStopped()

Description copied from interface: Stoppable

Returns True if Stoppable.stop(String) has been closed.

Specified by:

isStopped in interface Stoppable

cleanupReplicaReplicaStaleCache

private void cleanupReplicaReplicaStaleCache()

refreshCatalogReplicaCount

private int refreshCatalogReplicaCount()

getCacheCleanupChore

private ScheduledChore getCacheCleanupChore(CatalogReplicaLoadBalanceSimpleSelector selector)

getRefreshReplicaCountChore

private ScheduledChore getRefreshReplicaCountChore(CatalogReplicaLoadBalanceSimpleSelector selector)