CatalogReplicaLoadBalanceSimpleSelector (Apache HBase 2.5.0 API)

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 and Description
`private static class`	`CatalogReplicaLoadBalanceSimpleSelector.StaleLocationCacheEntry` StaleLocationCacheEntry is the entry when a stale location is reported by an client.

Field Summary

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

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

Constructor Summary

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

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and 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 Detail
  - 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 Detail
  - CatalogReplicaLoadBalanceSimpleSelector
```
CatalogReplicaLoadBalanceSimpleSelector(TableName tableName,
                                        ChoreService choreService,
                                        IntSupplier getNumOfReplicas)
```
- Method Detail
  - 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)
```

Class CatalogReplicaLoadBalanceSimpleSelector

Nested Class Summary

Field Summary

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

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

LOG

STALE_CACHE_TIMEOUT_IN_MILLISECONDS

STALE_CACHE_CLEAN_CHORE_INTERVAL_IN_MILLISECONDS

REFRESH_REPLICA_COUNT_CHORE_INTERVAL_IN_MILLISECONDS

staleCache

numOfReplicas

choreService

tableName

getNumOfReplicas

isStopped

Constructor Detail

CatalogReplicaLoadBalanceSimpleSelector

Method Detail

onError

getRandomReplicaId

select

stop

isStopped

cleanupReplicaReplicaStaleCache

refreshCatalogReplicaCount

getCacheCleanupChore

getRefreshReplicaCountChore