Berkeley DB
version 4.8.30

com.sleepycat.collections
Class TransactionRunner

java.lang.Object
  extended by com.sleepycat.collections.TransactionRunner

public class TransactionRunner
extends Object

Starts a transaction, calls TransactionWorker.doWork(), and handles transaction retry and exceptions. To perform a transaction, the user implements the TransactionWorker interface and passes an instance of that class to the run method.

A single TransactionRunner instance may be used by any number of threads for any number of transactions.

The behavior of the run() method depends on whether the environment is transactional, whether nested transactions are enabled, and whether a transaction is already active.

In a transactional environment, the rules described above support nested calls to the run() method and guarantee that the outermost call will cause the transaction to be committed or aborted. This is true whether or not nested transactions are supported or enabled. Note that nested transactions are provided as an optimization for improving concurrency but do not change the meaning of the outermost transaction. Nested transactions are not currently supported by the JE product.


Field Summary
static int DEFAULT_MAX_RETRIES
          The default maximum number of retries.
 
Constructor Summary
TransactionRunner(Environment env)
          Creates a transaction runner for a given Berkeley DB environment.
TransactionRunner(Environment env, int maxRetries, TransactionConfig config)
          Creates a transaction runner for a given Berkeley DB environment and with a given number of maximum retries.
 
Method Summary
 boolean getAllowNestedTransactions()
          Returns whether nested transactions will be created if run() is called when a transaction is already active for the current thread.
 int getMaxRetries()
          Returns the maximum number of retries that will be performed when deadlocks are detected.
 TransactionConfig getTransactionConfig()
          Returns the transaction configuration used for calling Environment.beginTransaction(com.sleepycat.db.Transaction, com.sleepycat.db.TransactionConfig).
 int handleException(Exception exception, int retries, int maxRetries)
          Handles exceptions that occur during a transaction, and may implement transaction retry policy.
 void run(TransactionWorker worker)
          Calls the TransactionWorker.doWork() method and, for transactional environments, may begin and end a transaction.
 void setAllowNestedTransactions(boolean allowNestedTxn)
          Changes whether nested transactions will be created if run() is called when a transaction is already active for the current thread.
 void setMaxRetries(int maxRetries)
          Changes the maximum number of retries that will be performed when deadlocks are detected.
 void setTransactionConfig(TransactionConfig config)
          Changes the transaction configuration used for calling Environment.beginTransaction(com.sleepycat.db.Transaction, com.sleepycat.db.TransactionConfig).
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

DEFAULT_MAX_RETRIES

public static final int DEFAULT_MAX_RETRIES
The default maximum number of retries.

See Also:
Constant Field Values
Constructor Detail

TransactionRunner

public TransactionRunner(Environment env)
Creates a transaction runner for a given Berkeley DB environment. The default maximum number of retries (DEFAULT_MAX_RETRIES) and a null (default) TransactionConfig will be used.

Parameters:
env - is the environment for running transactions.

TransactionRunner

public TransactionRunner(Environment env,
                         int maxRetries,
                         TransactionConfig config)
Creates a transaction runner for a given Berkeley DB environment and with a given number of maximum retries.

Parameters:
env - is the environment for running transactions.
maxRetries - is the maximum number of retries that will be performed when deadlocks are detected.
config - the transaction configuration used for calling Environment.beginTransaction(com.sleepycat.db.Transaction, com.sleepycat.db.TransactionConfig), or null to use the default configuration. The configuration object is not cloned, and any modifications to it will impact subsequent transactions.
Method Detail

getMaxRetries

public int getMaxRetries()
Returns the maximum number of retries that will be performed when deadlocks are detected.


setMaxRetries

public void setMaxRetries(int maxRetries)
Changes the maximum number of retries that will be performed when deadlocks are detected. Calling this method does not impact transactions already running.


getAllowNestedTransactions

public boolean getAllowNestedTransactions()
Returns whether nested transactions will be created if run() is called when a transaction is already active for the current thread. By default this property is false.

Note that this method always returns false in the JE product, since nested transactions are not supported by JE.


setAllowNestedTransactions

public void setAllowNestedTransactions(boolean allowNestedTxn)
Changes whether nested transactions will be created if run() is called when a transaction is already active for the current thread. Calling this method does not impact transactions already running.

Note that true may not be passed to this method in the JE product, since nested transactions are not supported by JE.


getTransactionConfig

public TransactionConfig getTransactionConfig()
Returns the transaction configuration used for calling Environment.beginTransaction(com.sleepycat.db.Transaction, com.sleepycat.db.TransactionConfig).

If this property is null, the default configuration is used. The configuration object is not cloned, and any modifications to it will impact subsequent transactions.

Returns:
the transaction configuration.

setTransactionConfig

public void setTransactionConfig(TransactionConfig config)
Changes the transaction configuration used for calling Environment.beginTransaction(com.sleepycat.db.Transaction, com.sleepycat.db.TransactionConfig).

If this property is null, the default configuration is used. The configuration object is not cloned, and any modifications to it will impact subsequent transactions.

Parameters:
config - the transaction configuration.

run

public void run(TransactionWorker worker)
         throws DatabaseException,
                Exception
Calls the TransactionWorker.doWork() method and, for transactional environments, may begin and end a transaction. If the environment given is non-transactional, a transaction will not be used but the doWork() method will still be called. See the class description for more information.

Throws:
DeadlockException - when it is thrown by doWork() and the maximum number of retries has occurred. The transaction will have been aborted by this method.
Exception - when any other exception is thrown by doWork(). The exception will first be unwrapped by calling ExceptionUnwrapper.unwrap(java.lang.Exception). The transaction will have been aborted by this method.
DatabaseException

handleException

public int handleException(Exception exception,
                           int retries,
                           int maxRetries)
                    throws Exception
Handles exceptions that occur during a transaction, and may implement transaction retry policy. The transaction is aborted by the run method before calling this method.

The default implementation of this method throws the exception parameter if it is not an instance of DeadlockException and otherwise returns the maxRetries parameter value. This method can be overridden to throw a different exception or return a different number of retries. For example:

Parameters:
exception - an exception that was thrown by the TransactionWorker.doWork() method or thrown when beginning or committing the transaction. If the retries value is greater or equal to maxRetries when this method returns normally, this exception will be thrown by the run method.
retries - the current value of a counter that starts out at zero and is incremented when each retry is performed.
maxRetries - the maximum retries to be performed. By default, this value is set to getMaxRetries(). This method may return a different maximum retries value to override that default.
Returns:
the maximum number of retries to perform. The default policy is to return the maxRetries parameter value if the exception parameter value is an instance of DeadlockException.
Throws:
Exception - to cause the exception to be thrown by the run method. The default policy is to throw the exception parameter value if it is not an instance of DeadlockException.
Since:
3.4

Berkeley DB
version 4.8.30

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