FSHLog.RingBufferEventHandler (Apache HBase 1.2.12 API)

java.lang.Object
- org.apache.hadoop.hbase.regionserver.wal.FSHLog.RingBufferEventHandler

All Implemented Interfaces:

com.lmax.disruptor.EventHandler<RingBufferTruck>, com.lmax.disruptor.LifecycleAware

Enclosing class:

FSHLog
```
 class FSHLog.RingBufferEventHandler
extends Object
implements com.lmax.disruptor.EventHandler<RingBufferTruck>, com.lmax.disruptor.LifecycleAware
```
Handler that is run by the disruptor ringbuffer consumer. Consumer is a SINGLE 'writer/appender' thread. Appends edits and starts up sync runs. Tries its best to batch up syncs. There is no discernible benefit batching appends so we just append as they come in because it simplifies the below implementation. See metrics for batching effectiveness (In measurement, at 100 concurrent handlers writing 1k, we are batching > 10 appends and 10 handler sync invocations for every actual dfsclient sync call; at 10 concurrent handlers, YMMV).
Herein, we have an array into which we store the sync futures as they come in. When we have a 'batch', we'll then pass what we have collected to a SyncRunner thread to do the filesystem sync. When it completes, it will then call SyncFuture.done(long, Throwable) on each of SyncFutures in the batch to release blocked Handler threads.
I've tried various effects to try and make latencies low while keeping throughput high. I've tried keeping a single Queue of SyncFutures in this class appending to its tail as the syncs coming and having sync runner threads poll off the head to 'finish' completed SyncFutures. I've tried linkedlist, and various from concurrent utils whether LinkedBlockingQueue or ArrayBlockingQueue, etc. The more points of synchronization, the more 'work' (according to 'perf stats') that has to be done; small increases in stall percentages seem to have a big impact on throughput/latencies. The below model where we have an array into which we stash the syncs and then hand them off to the sync thread seemed like a decent compromise. See HBASE-8755 for more detail.

Field Summary

Fields
Modifier and Type	Field and Description
`private Exception`	`exception` Set if we get an exception appending or syncing so that all subsequence appends and syncs on this WAL fail until WAL is replaced.
`private Object`	`safePointWaiter` Object to block on while waiting on safe point.
`private boolean`	`shutdown`
`private SyncFuture[]`	`syncFutures`
`private int`	`syncFuturesCount`
`private int`	`syncRunnerIndex` Which syncrunner to use next.
`private FSHLog.SyncRunner[]`	`syncRunners`
`private FSHLog.SafePointZigZagLatch`	`zigzagLatch`

Constructor Summary

Constructors
Constructor and Description

FSHLog.RingBufferEventHandler(int syncRunnerCount, int maxHandlersCount)

Constructors
Constructor and Description
`FSHLog.RingBufferEventHandler(int syncRunnerCount, int maxHandlersCount)`

Method Summary

Methods
Modifier and Type	Method and Description
`(package private) void`	`append(FSWALEntry entry)` Append to the WAL.
`(package private) FSHLog.SafePointZigZagLatch`	`attainSafePoint()`
`private void`	`attainSafePoint(long currentSequence)` Check if we should attain safe point.
`private void`	`cleanupOutstandingSyncsOnException(long sequence, Exception e)`
`private boolean`	`isOutstandingSyncs()`
`private boolean`	`isOutstandingSyncsFromRunners()`
`void`	`onEvent(RingBufferTruck truck, long sequence, boolean endOfBatch)`
`void`	`onShutdown()`
`void`	`onStart()`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

syncRunners

private final FSHLog.SyncRunner[] syncRunners

syncFutures
```
private final SyncFuture[] syncFutures
```

syncFuturesCount
```
private volatile int syncFuturesCount
```

zigzagLatch

private volatile FSHLog.SafePointZigZagLatch zigzagLatch

exception
```
private Exception exception
```
Set if we get an exception appending or syncing so that all subsequence appends and syncs on this WAL fail until WAL is replaced.

safePointWaiter
```
private final Object safePointWaiter
```
Object to block on while waiting on safe point.

shutdown
```
private volatile boolean shutdown
```

syncRunnerIndex
```
private int syncRunnerIndex
```
Which syncrunner to use next.

Constructor Detail

FSHLog.RingBufferEventHandler

FSHLog.RingBufferEventHandler(int syncRunnerCount,
                             int maxHandlersCount)

Method Detail
- cleanupOutstandingSyncsOnException
```
private void cleanupOutstandingSyncsOnException(long sequence,
                                      Exception e)
```
- isOutstandingSyncs
```
private boolean isOutstandingSyncs()
```
  Returns:
  True if outstanding sync futures still
- isOutstandingSyncsFromRunners
```
private boolean isOutstandingSyncsFromRunners()
```
- onEvent
```
public void onEvent(RingBufferTruck truck,
           long sequence,
           boolean endOfBatch)
             throws Exception
```
  Specified by:
  
  onEvent in interface com.lmax.disruptor.EventHandler<RingBufferTruck>
  
  Throws:
  
  Exception
- attainSafePoint
```
FSHLog.SafePointZigZagLatch attainSafePoint()
```
- attainSafePoint
```
private void attainSafePoint(long currentSequence)
```
  Check if we should attain safe point. If so, go there and then wait till signalled before we proceeding.
- append
```
void append(FSWALEntry entry)
      throws Exception
```
  Append to the WAL. Does all CP and WAL listener calls.
  
  Parameters:
  entry -
  
  Throws:
  
  Exception
- onStart
```
public void onStart()
```
  Specified by:
  
  onStart in interface com.lmax.disruptor.LifecycleAware
- onShutdown
```
public void onShutdown()
```
  Specified by:
  
  onShutdown in interface com.lmax.disruptor.LifecycleAware

Class FSHLog.RingBufferEventHandler

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

syncRunners

syncFutures

syncFuturesCount

zigzagLatch

exception

safePointWaiter

shutdown

syncRunnerIndex

Constructor Detail

FSHLog.RingBufferEventHandler

Method Detail

cleanupOutstandingSyncsOnException

isOutstandingSyncs

isOutstandingSyncsFromRunners

onEvent

attainSafePoint

attainSafePoint

append

onStart

onShutdown