com.sleepycat.je

Class Sequence

java.lang.Object

com.sleepycat.je.Sequence

public class Sequence
extends java.lang.Object

A Sequence handle is used to manipulate a sequence record in a database. Sequence handles are opened using the Database.openSequence method.

Constructor Summary

Constructors

Constructor and Description
Sequence(Database db, Transaction txn, DatabaseEntry key, SequenceConfig config) Opens a sequence handle, adding the sequence record if appropriate.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Closes a sequence.
long	get(Transaction txn, int delta) Returns the next available element in the sequence and changes the sequence value by delta.
Database	getDatabase() Returns the Database handle associated with this sequence.
DatabaseEntry	getKey() Returns the DatabaseEntry used to open this sequence.
SequenceStats	getStats(StatsConfig config) Returns statistical information about the sequence.

Methods inherited from class java.lang.Object

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

Constructor Detail

Sequence

Sequence(Database db,
        Transaction txn,
        DatabaseEntry key,
        SequenceConfig config)
   throws DatabaseException

Opens a sequence handle, adding the sequence record if appropriate.

Throws:

DatabaseException

Method Detail

close

public void close()
           throws DatabaseException

Closes a sequence. Any unused cached values are lost.

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

Throws:

DatabaseException - if a failure occurs.

get

public long get(Transaction txn,
       int delta)
         throws DatabaseException

Returns the next available element in the sequence and changes the sequence value by delta. The value of delta must be greater than zero. If there are enough cached values in the sequence handle then they will be returned. Otherwise the next value will be fetched from the database and incremented (decremented) by enough to cover the delta and the next batch of cached values. This method is synchronized to protect updating of the cached value, since multiple threads may share a single handle. Multiple handles for the same database/key may be used to increase concurrency.

The txn handle must be null if the sequence handle was opened with a non-zero cache size.

For maximum concurrency, a non-zero cache size should be specified prior to opening the sequence handle, the txn handle should be null, and SequenceConfig.setAutoCommitNoSync should be called to disable log flushes.

Parameters:

txn - For a transactional database, an explicit transaction may be specified, or null may be specified to use auto-commit. For a non-transactional database, null must be specified.

delta - the amount by which to increment or decrement the sequence

Returns:

the next available element in the sequence

Throws:

DatabaseException

getDatabase

public Database getDatabase()
                     throws DatabaseException

Returns the Database handle associated with this sequence.

Returns:

The Database handle associated with this sequence.

Throws:

DatabaseException

getKey

public DatabaseEntry getKey()
                     throws DatabaseException

Returns the DatabaseEntry used to open this sequence.

Returns:

The DatabaseEntry used to open this sequence.

Throws:

DatabaseException

getStats

public SequenceStats getStats(StatsConfig config)
                       throws DatabaseException

Returns statistical information about the sequence.

In the presence of multiple threads or processes accessing an active sequence, the information returned by this method may be out-of-date.

The getStats method cannot be transaction-protected. For this reason, it should be called in a thread of control that has no open cursors or active transactions.

Parameters:

config - The statistics returned; if null, default statistics are returned.

Returns:

Sequence statistics.

Throws:

DatabaseException