com.persistit

Class Accumulator.SeqAccumulator

java.lang.Object

com.persistit.Accumulator

com.persistit.Accumulator.SeqAccumulator

Enclosing class:

Accumulator

public static final class Accumulator.SeqAccumulator
extends Accumulator

An Accumulator used to generate unique ID values. The allocate() method generates a new, unique long value. The transaction records this value as a candidate for maximum value of the Accumulator. On recovery, the highest such value ever allocated by a committed transaction is recovered, and so after recovery the next allocated ID value will be larger than any previously consumed.

Nested Class Summary

Nested classes/interfaces inherited from class com.persistit.Accumulator

Accumulator.MaxAccumulator, Accumulator.MinAccumulator, Accumulator.SeqAccumulator, Accumulator.SumAccumulator, Accumulator.Type

Field Summary

Fields inherited from class com.persistit.Accumulator

_tree

Method Summary

Modifier and Type	Method and Description
long	allocate() Allocate a sequence number.

Methods inherited from class com.persistit.Accumulator

getLiveValue, getSnapshotValue, toString

Methods inherited from class java.lang.Object

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

Method Detail

allocate

public long allocate()

Allocate a sequence number. The value returned is guaranteed to be unique for the lifetime of the database. Values are usually assigned as consecutive integers, but in some cases there may be gaps in the sequence.

The value returned is equal to the live value the instant it is updated. However, note that the following code is not guaranteed to generate a unique value:

    seqAccumulator.allocate();
    long id = seqAccumulator.getLiveValue();
 

while the following is:

   long id = seqAccumulator.allocate();
 

Returns:

the updated live value