com.sleepycat.db
Class Transaction

java.lang.Object
  com.sleepycat.db.Transaction

public class Transaction

extends Object

The Transaction object is the handle for a transaction. Methods off the transaction handle are used to configure, abort and commit the transaction. Transaction handles are provided to other Berkeley DB methods in order to transactionally protect those operations.

Transaction handles are not free-threaded; transactions handles may be used by multiple threads, but only serially, that is, the application must serialize access to the handle. Once the Transaction.abort, Transaction.commit or Transaction.discard methods are called, the handle may not be accessed again, regardless of the success or failure of the method. In addition, parent transactions may not issue any Berkeley DB operations while they have active child transactions (child transactions that have not yet been committed or aborted) except for Environment.beginTransaction, Transaction.abort and Transaction.commit.

To obtain a transaction with default attributes:

    Transaction txn = myEnvironment.beginTransaction(null, null);

To customize the attributes of a transaction:

    TransactionConfig config = new TransactionConfig();
    config.setDirtyRead(true);
    Transaction txn = myEnvironment.beginTransaction(null, config);

Method Summary

void	abort() Cause an abnormal termination of the transaction.
void	commit() End the transaction.
void	commitNoSync() End the transaction, not committing synchronously.
void	commitSync() End the transaction, committing synchronously.
void	commitWriteNoSync() End the transaction, writing but not flushing the log.
void	discard() Free up all the per-process resources associated with the specified Transaction handle, neither committing nor aborting the transaction.
int	getId() Return the transaction's unique ID.
void	prepare(byte[] gid) Initiate the beginning of a two-phase commit.
void	setLockTimeout(long timeOut) Configure the lock request timeout value for the transaction.
void	setTxnTimeout(long timeOut) Configure the timeout value for the transaction lifetime.

Methods inherited from class java.lang.Object

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

Method Detail

getId

public int getId()
          throws DatabaseException

Return the transaction's unique ID.

Locking calls made on behalf of this transaction should use the value returned from this method as the locker parameter to the Environment.getLock or Environment.lockVector calls.

Returns:

The transaction's unique ID.

Throws:

DatabaseException - if a failure occurs.

abort

public void abort()
           throws DatabaseException

Cause an abnormal termination of the transaction.

The log is played backward, and any necessary undo operations are done. Before Transaction.abort returns, any locks held by the transaction will have been released.

In the case of nested transactions, aborting a parent transaction causes all children (unresolved or not) of the parent transaction to be aborted.

All cursors opened within the transaction must be closed before the transaction is aborted.

After Transaction.abort has been called, regardless of its return, the Transaction handle may not be accessed again.

Throws:

DatabaseException - if a failure occurs.

commit

public void commit()
            throws DatabaseException

End the transaction. If the environment is configured for synchronous commit, the transaction will be committed synchronously to stable storage before the call returns. This means the transaction will exhibit all of the ACID (atomicity, consistency, isolation, and durability) properties.

If the environment is not configured for synchronous commit, the commit will not necessarily have been committed to stable storage before the call returns. This means the transaction will exhibit the ACI (atomicity, consistency, and isolation) properties, but not D (durability); that is, database integrity will be maintained, but it is possible this transaction may be undone during recovery.

In the case of nested transactions, if the transaction is a parent transaction, committing the parent transaction causes all unresolved children of the parent to be committed. In the case of nested transactions, if the transaction is a child transaction, its locks are not released, but are acquired by its parent. Although the commit of the child transaction will succeed, the actual resolution of the child transaction is postponed until the parent transaction is committed or aborted; that is, if its parent transaction commits, it will be committed; and if its parent transaction aborts, it will be aborted.

All cursors opened within the transaction must be closed before the transaction is committed.

After this method returns the Transaction handle may not be accessed again, regardless of the method's success or failure. If the method encounters an error, the transaction and all child transactions of the transaction will have been aborted when the call returns.

Throws:

DatabaseException - if a failure occurs.

commitSync

public void commitSync()
                throws DatabaseException

End the transaction, committing synchronously. This means the transaction will exhibit all of the ACID (atomicity, consistency, isolation, and durability) properties.

This behavior is the default for database environments unless otherwise configured using the EnvironmentConfig.setTxnNoSync method. This behavior may also be set for a single transaction using the Environment.beginTransaction method. Any value specified to this method overrides both of those settings.

In the case of nested transactions, if the transaction is a parent transaction, committing the parent transaction causes all unresolved children of the parent to be committed. In the case of nested transactions, if the transaction is a child transaction, its locks are not released, but are acquired by its parent. Although the commit of the child transaction will succeed, the actual resolution of the child transaction is postponed until the parent transaction is committed or aborted; that is, if its parent transaction commits, it will be committed; and if its parent transaction aborts, it will be aborted.

All cursors opened within the transaction must be closed before the transaction is committed.

After this method returns the Transaction handle may not be accessed again, regardless of the method's success or failure. If the method encounters an error, the transaction and all child transactions of the transaction will have been aborted when the call returns.

Throws:

DatabaseException - if a failure occurs.

commitNoSync

public void commitNoSync()
                  throws DatabaseException

End the transaction, not committing synchronously. This means the transaction will exhibit the ACI (atomicity, consistency, and isolation) properties, but not D (durability); that is, database integrity will be maintained, but it is possible this transaction may be undone during recovery.

This behavior may be set for a database environment using the EnvironmentConfig.setTxnNoSync method or for a single transaction using the Environment.beginTransaction method. Any value specified to this method overrides both of those settings.

In the case of nested transactions, if the transaction is a parent transaction, committing the parent transaction causes all unresolved children of the parent to be committed. In the case of nested transactions, if the transaction is a child transaction, its locks are not released, but are acquired by its parent. Although the commit of the child transaction will succeed, the actual resolution of the child transaction is postponed until the parent transaction is committed or aborted; that is, if its parent transaction commits, it will be committed; and if its parent transaction aborts, it will be aborted.

All cursors opened within the transaction must be closed before the transaction is committed.

After this method returns the Transaction handle may not be accessed again, regardless of the method's success or failure. If the method encounters an error, the transaction and all child transactions of the transaction will have been aborted when the call returns.

Throws:

DatabaseException - if a failure occurs.

commitWriteNoSync

public void commitWriteNoSync()
                       throws DatabaseException

End the transaction, writing but not flushing the log. This means the transaction will exhibit the ACI (atomicity, consistency, and isolation) properties, but not D (durability); that is, database integrity will be maintained, but it is possible this transaction may be undone during recovery in the event that the operating system crashes. This option provides more durability than an asynchronous commit and has less performance cost than a synchronous commit.

This behavior may be set for a database environment using the EnvironmentConfig.setTxnWriteNoSync method or for a single transaction using the Environment.beginTransaction method. Any value specified to this method overrides both of those settings.

In the case of nested transactions, if the transaction is a parent transaction, committing the parent transaction causes all unresolved children of the parent to be committed. In the case of nested transactions, if the transaction is a child transaction, its locks are not released, but are acquired by its parent. Although the commit of the child transaction will succeed, the actual resolution of the child transaction is postponed until the parent transaction is committed or aborted; that is, if its parent transaction commits, it will be committed; and if its parent transaction aborts, it will be aborted.

All cursors opened within the transaction must be closed before the transaction is committed.

After this method returns the Transaction handle may not be accessed again, regardless of the method's success or failure. If the method encounters an error, the transaction and all child transactions of the transaction will have been aborted when the call returns.

Throws:

DatabaseException - if a failure occurs.

setTxnTimeout

public void setTxnTimeout(long timeOut)
                   throws DatabaseException

Configure the timeout value for the transaction lifetime.

If the transaction runs longer than this time, the transaction may may throw DatabaseException.

Timeouts are checked whenever a thread of control blocks on a lock or when deadlock detection is performed. For this reason, the accuracy of the timeout depends on how often deadlock detection is performed.

Parameters:

timeOut - The timeout value for the transaction lifetime, in microseconds. As the value is an unsigned 32-bit number of microseconds, the maximum timeout is roughly 71 minutes. A value of 0 disables timeouts for the transaction.

This method may be called at any time during the life of the application.

Throws:

DatabaseException - if a failure occurs.

setLockTimeout

public void setLockTimeout(long timeOut)
                    throws DatabaseException

Configure the lock request timeout value for the transaction.

If a lock request cannot be granted in this time, the transaction may throw DatabaseException.

Timeouts are checked whenever a thread of control blocks on a lock or when deadlock detection is performed. For this reason, the accuracy of the timeout depends on how often deadlock detection is performed.

Parameters:

timeOut - The lock request timeout value for the transaction, in microseconds. As the value is an unsigned 32-bit number of microseconds, the maximum timeout is roughly 71 minutes. A value of 0 disables timeouts for the transaction.

This method may be called at any time during the life of the application.

Throws:

DatabaseException - if a failure occurs.

discard

public void discard()
             throws DatabaseException

Free up all the per-process resources associated with the specified Transaction handle, neither committing nor aborting the transaction. This call may be used only after calls to Environment.recover when there are multiple global transaction managers recovering transactions in a single database environment. Any transactions returned by Environment.recover that are not handled by the current global transaction manager should be discarded using this method.

The Transaction handle may not be accessed again after this method has been called, regardless of the method's success or failure.

Throws:

DatabaseException - if a failure occurs.

prepare

public void prepare(byte[] gid)
             throws DatabaseException

Initiate the beginning of a two-phase commit.

In a distributed transaction environment, Berkeley DB can be used as a local transaction manager. In this case, the distributed transaction manager must send prepare messages to each local manager. The local manager must then issue a Transaction.prepare call and await its successful return before responding to the distributed transaction manager. Only after the distributed transaction manager receives successful responses from all of its prepare messages should it issue any commit messages.

In the case of nested transactions, preparing the parent causes all unresolved children of the parent transaction to be committed. Child transactions should never be explicitly prepared. Their fate will be resolved along with their parent's during global recovery.

Parameters:

gid - The global transaction ID by which this transaction will be known. This global transaction ID will be returned in calls to Environment.recover method, telling the application which global transactions must be resolved. The gid parameter must be sized at least DB_XIDDATASIZE (currently 128) bytes; only the first DB_XIDDATASIZE bytes are used.

Throws:

DatabaseException - if a failure occurs.