com.bigdata.journal

Class WriteExecutorService

java.lang.Object

java.util.concurrent.AbstractExecutorService

java.util.concurrent.ThreadPoolExecutor

com.bigdata.journal.WriteExecutorService

All Implemented Interfaces:

Executor, ExecutorService

public class WriteExecutorService
extends ThreadPoolExecutor

A custom ThreadPoolExecutor used by the ConcurrencyManager to execute concurrent unisolated write tasks and perform group commits. Tasks extend AbstractTask. The caller receives a Future when they submit a task to the write service. That Future is NOT available until the next group commit following the successful execution of the write task.

Note: adding the thread name to the log messages for this class can aid debugging. You can do this using the log4j configuration.

Note: the problem with running concurrent unisolated operations during a commit and relying on an "auto-commit" flag to indicate whether or not the index will participate is two fold. First, previous unisolated operations on the same index will not get committed if an operation is currently running, so we could wind up deferring check points of indices for quite a while. Second, if there is a problem with the commit and we have to abort, then any ongoing operations would still be using unisolated indices that could include write sets that were discarded - this would make abort non-atomic.

The ground state from which an unisolated operation begins needs to evolve after each unisolated operation that reaches its commit point successfully. This can be accomplished by holding onto the btree reference, or even just the address at which the metadata record for the btree was last written. We use AbstractJournal.getName2Addr() for this purpose.

However, if an unisolated write fails for any reason on a given index then we MUST use the last successful check point for that index. This is handled by doing an abort.

Note: Due to the way in which the BTree class is written, it "steals" child references when cloning an immutable node or leaf prior to making modifications. This means that we must reload the btree from a metadata record if we have to roll back due to an abort of some unisolated operation since the state of the BTree has been changed as a side effect in a non-reversible manner.

Note: Running Threads may be interrupted at arbitrary moments for a number of reasons by this class. The foremost example is a Thread that is executing an AbstractTask when a concurrent decision is made to discard the commit group, e.g., because another task in that commit group failed. Regardless of the reason, if the Thread is performing an NIO operation at the moment that the interrupt is notice, then it will close the channel on which that operation was being performed. If you are using a disk-based BufferMode for the journal, then the interrupt just caused the backing FileChannel to be closed. In order to permit continued operations on the journal, the IRawStore MUST transparently re-open the channel. (The same problem can arise if you are using NIO for sockets or anything else that uses the Channel abstraction.)

Overflow handling

The WriteExecutorService invokes #overflow() each time it does a group commit. Normally the WriteExecutorService does not quiesce before doing a group commit, and when it is not quiescent the ResourceManager can NOT #overflow() the journal since concurrent tasks are still writing on the current journal. Therefore the ResourceManager monitors the IBufferStrategy.getExtent() of the live journal. When it decides that the live journal is large enough it pause()s WriteExecutorService and waits until #overflow() is called with a quiescent WriteExecutorService. This effectively grants the ResourceManager exclusive access to the journal. It can then run #overflow() to setup a new journal and tell the WriteExecutorService to resume() processing.

Author:

Bryan Thompson

Nested Class Summary

Nested classes/interfaces inherited from class java.util.concurrent.ThreadPoolExecutor

ThreadPoolExecutor.AbortPolicy, ThreadPoolExecutor.CallerRunsPolicy, ThreadPoolExecutor.DiscardOldestPolicy, ThreadPoolExecutor.DiscardPolicy

Field Summary

Fields

Modifier and Type	Field and Description
protected AtomicInteger	activeTaskCountWithLocksHeld
protected long	groupCommitTimeout The time in milliseconds that a group commit will await currently running tasks to join the commit group.
protected long	overflowLockRequestTimeout The time in milliseconds that a group commit will await an exclusive lock on the write service in order to perform synchronous overflow processing.
protected static org.apache.log4j.Logger	overflowLog Uses the OverflowManager log for things relating to synchronous overflow processing.

Constructor Summary

Constructors

Constructor and Description
WriteExecutorService(IResourceManager resourceManager, int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit keepAliveUnit, BlockingQueue<Runnable> queue, ThreadFactory threadFactory, long groupCommitTimeout, long overflowLockRequestTimeout)

Method Summary

Methods

Modifier and Type	Method and Description
protected void	afterTask(AbstractTask<?> r, Throwable t) This is executed after AbstractTask.doTask().
protected void	beforeExecute(Thread t, Runnable r) If task execution has been paused then awaits someone to call resume().
protected void	beforeTask(Thread t, AbstractTask<?> r) Executed before AbstractTask.doTask()
long	getAbortCount() The #of aborts (not failed tasks) since the WriteExecutorService was started.
int	getActiveTaskCountWithLocksHeld() The instantaneous #of tasks that have acquired their locks are executing concurrently on the write service.
long	getByteCountPerCommit() The #of bytes written by the last commit.
int	getCommitGroupSize() The #of tasks in the most recent commit group.
long	getGroupCommitCount() The #of group commits since the WriteExecutorService was started (all commits by this service are group commits).
int	getInternalLockQueueLength() The #of threads queued on the internal lock.
NonBlockingLockManagerWithNewDesign<String>	getLockManager() The object that coordinates exclusive access to the resources.
int	getMaxCommitGroupSize() The maximum #of tasks in any commit group.
long	getMaxCommitServiceTime() The maximum service time in milliseconds of the atomic commit.
long	getMaxCommitWaitingTime() The maximum waiting time in millseconds from when a task completes successfully until the next group commit.
int	getMaxPoolSize() The maximum #of threads in the pool.
long	getMaxRunning() The maximum #of tasks that are concurrently executing without regard to whether or not the tasks have acquired their locks.
long	getOverflowCount() The #of times synchronous overflow processing has been performed.
int	getReadyCount() #of tasks that are waiting to run but are blocked on the #lock.
long	getRejectedExecutionCount() The #of rejected tasks.
long	getTaskCommittedCount() The #of tasks that (a) executed successfully and (b) have been committed.
long	getTaskFailedCount() The #of tasks that have failed.
long	getTaskSuccessCount() The #of tasks that have executed successfully (MIGHT NOT have been committed safely).
void	shutdown() Overridden to shutdown the embedded lock manager service.
List<Runnable>	shutdownNow() Overridden to shutdown the embedded lock manager service.
String	toString() A snapshot of the executor state.
boolean	tryLock(long timeout, TimeUnit unit) Acquires an exclusive lock on the write service.
void	unlock() Release the exclusive write lock.

Methods inherited from class java.util.concurrent.ThreadPoolExecutor

afterExecute, allowCoreThreadTimeOut, allowsCoreThreadTimeOut, awaitTermination, execute, finalize, getActiveCount, getCompletedTaskCount, getCorePoolSize, getKeepAliveTime, getLargestPoolSize, getMaximumPoolSize, getPoolSize, getQueue, getRejectedExecutionHandler, getTaskCount, getThreadFactory, isShutdown, isTerminated, isTerminating, prestartAllCoreThreads, prestartCoreThread, purge, remove, setCorePoolSize, setKeepAliveTime, setMaximumPoolSize, setRejectedExecutionHandler, setThreadFactory, terminated

Methods inherited from class java.util.concurrent.AbstractExecutorService

invokeAll, invokeAll, invokeAny, invokeAny, newTaskFor, newTaskFor, submit, submit, submit

Methods inherited from class java.lang.Object

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

Field Detail

overflowLog

protected static final org.apache.log4j.Logger overflowLog

Uses the OverflowManager log for things relating to synchronous overflow processing.

groupCommitTimeout

protected final long groupCommitTimeout

The time in milliseconds that a group commit will await currently running tasks to join the commit group.

overflowLockRequestTimeout

protected final long overflowLockRequestTimeout

The time in milliseconds that a group commit will await an exclusive lock on the write service in order to perform synchronous overflow processing. This lock is requested IFF overflow process SHOULD be performed. The lock timeout needs to be of significant duration or a lock request for a write service under heavy write load will timeout, in which case an error will be logged. If overflow processing is not performed the live journal extent will grow without bound.

activeTaskCountWithLocksHeld

protected final AtomicInteger activeTaskCountWithLocksHeld

Constructor Detail

WriteExecutorService

public WriteExecutorService(IResourceManager resourceManager,
                    int corePoolSize,
                    int maximumPoolSize,
                    long keepAliveTime,
                    TimeUnit keepAliveUnit,
                    BlockingQueue<Runnable> queue,
                    ThreadFactory threadFactory,
                    long groupCommitTimeout,
                    long overflowLockRequestTimeout)

Parameters:

resourceManager -

corePoolSize -

maximumPoolSize -

keepAliveTime -

keepAliveUnit -

queue -

threadFactory -

groupCommitTimeout - The time in milliseconds that a group commit will await currently running tasks to join the commit group.

overflowLockRequestTimeout -

Method Detail

getLockManager

public NonBlockingLockManagerWithNewDesign<String> getLockManager()

The object that coordinates exclusive access to the resources.

getRejectedExecutionCount

public long getRejectedExecutionCount()

The #of rejected tasks.

getMaxPoolSize

public int getMaxPoolSize()

The maximum #of threads in the pool.

getMaxRunning

public long getMaxRunning()

The maximum #of tasks that are concurrently executing without regard to whether or not the tasks have acquired their locks.

Note: Since this does not reflect tasks executing concurrently with locks held it is not a measure of the true concurrency of tasks executing on the service.

getMaxCommitWaitingTime

public long getMaxCommitWaitingTime()

The maximum waiting time in millseconds from when a task completes successfully until the next group commit.

getMaxCommitServiceTime

public long getMaxCommitServiceTime()

The maximum service time in milliseconds of the atomic commit.

See Also:

AbstractJournal.commit()

getInternalLockQueueLength

public int getInternalLockQueueLength()

The #of threads queued on the internal lock. These are (for the most part) threads waiting to start or stop during a group commit. However, you can not use this measure to infer whether there are threads waiting to run which are being starved during a group commit or simply threads waiting to do their post-processing.

getCommitGroupSize

public int getCommitGroupSize()

The #of tasks in the most recent commit group. In order to be useful information this must be sampled and turned into a moving average.

getMaxCommitGroupSize

public int getMaxCommitGroupSize()

The maximum #of tasks in any commit group.

getGroupCommitCount

public long getGroupCommitCount()

The #of group commits since the WriteExecutorService was started (all commits by this service are group commits).

getByteCountPerCommit

public long getByteCountPerCommit()

The #of bytes written by the last commit. This must be sampled to turn it into useful information.

getAbortCount

public long getAbortCount()

The #of aborts (not failed tasks) since the WriteExecutorService was started. Aborts are serious events and occur IFF an IAtomicStore.commit() fails. Failed tasks do NOT result in an abort.

getTaskFailedCount

public long getTaskFailedCount()

The #of tasks that have failed. Task failure means that the write set(s) for the task are discarded and any indices on which it has written are rolled back. Task failure does NOT cause the commit group to be discard. Rather, the failed task never joins a commit group and returns control immediately to the caller.

getTaskSuccessCount

public long getTaskSuccessCount()

The #of tasks that have executed successfully (MIGHT NOT have been committed safely).

See Also:

getTaskCommittedCount()

getTaskCommittedCount

public long getTaskCommittedCount()

The #of tasks that (a) executed successfully and (b) have been committed.

getOverflowCount

public long getOverflowCount()

The #of times synchronous overflow processing has been performed.

getActiveTaskCountWithLocksHeld

public int getActiveTaskCountWithLocksHeld()

The instantaneous #of tasks that have acquired their locks are executing concurrently on the write service. This is the real measure of concurrent task execution on the write service. However, you need to sample this value and compute a moving average in order to turn it into useful information.

The returned value is limited by ThreadPoolExecutor.getActiveCount(). Note that ThreadPoolExecutor.getActiveCount() reports tasks which are waiting on their locks as well as those engaged in various pre- or post-processing.

getReadyCount

public int getReadyCount()

#of tasks that are waiting to run but are blocked on the #lock. This value represents the #of tasks which have been starved from concurrent execution. The main culprit for a high value here is group commit and the occasional synchronous overflow or purge resources (when someone has an exclusive lock on the write service).

beforeExecute

protected void beforeExecute(Thread t,
                 Runnable r)

If task execution has been paused then awaits someone to call resume().

Overrides:

beforeExecute in class ThreadPoolExecutor

Parameters:

t - The thread that will run the task.

r - The Runnable wrapping the AbstractTask - this is actually a FutureTask. See AbstractExecutorService.

beforeTask

protected void beforeTask(Thread t,
              AbstractTask<?> r)

Executed before AbstractTask.doTask()

Parameters:

t - The thread in which that task will execute.

r - The AbstractTask.

afterTask

protected void afterTask(AbstractTask<?> r,
             Throwable t)

This is executed after AbstractTask.doTask(). If the task completed successfully (no exception thrown and its thread is not interrupted) then we invoke groupCommit(). Otherwise the write set of the task was already discarded by AbstractTask.InnerWriteServiceCallable and we do nothing.

Parameters:

r - The Callable wrapping the AbstractTask.

t - The exception thrown -or- null if the task completed successfully.

toString

public String toString()

A snapshot of the executor state.

Overrides:

toString in class ThreadPoolExecutor

shutdown

public void shutdown()

Overridden to shutdown the embedded lock manager service.

Specified by:

shutdown in interface ExecutorService

Overrides:

shutdown in class ThreadPoolExecutor

shutdownNow

public List<Runnable> shutdownNow()

Overridden to shutdown the embedded lock manager service.

Specified by:

shutdownNow in interface ExecutorService

Overrides:

shutdownNow in class ThreadPoolExecutor

tryLock

public boolean tryLock(long timeout,
              TimeUnit unit)
                throws InterruptedException

Acquires an exclusive lock on the write service.

The write service is paused for up to timeout units. During that time no new tasks will start. The lock will be granted if all running tasks complete before the timeout expires.

Note: The exclusive write lock is granted using the same lock that is used to coordinate all other activity of the write service. If the exclusive write lock is granted then the caller's thread will hold the lock and MUST release the lock using unlock().

Note: When the exclusive lock is granted there will be NO running tasks and the write service will be paused. This ensures that no task can run on the write service and that groupCommit will not attempt to grab the lock itself.

Note: If there is heavy write activity on the service then the timeout may well expire before the exclusive write lock becomes available. Further, the acquisition of the exclusive write lock will throttle concurrent write activity and negatively impact write performance if the system is heavily loaded by write tasks. Therefore, the write lock should be requested only when it is necessary and a significant value should be specified for the timeout (60s or more) to ensure that it is acquired.

Parameters:

timeout - The timeout.

unit - The unit in which the timeout is expressed.

Returns:

true iff the exclusive lock was acquired.

Throws:

InterruptedException

unlock

public void unlock()

Release the exclusive write lock.

Throws:

IllegalMonitorStateException - if the current thread does not own the lock.