org.agrona.concurrent

Class SnowflakeIdGenerator

java.lang.Object

org.agrona.concurrent.SnowflakeIdGenerator

All Implemented Interfaces:

IdGenerator

public final class SnowflakeIdGenerator
extends Object
implements IdGenerator

Generate unique identifiers based on the Twitter Snowflake algorithm.

This implementation is lock-less resulting in greater throughput plus less contention and latency jitter.

Note: ntpd, or alternative clock source, should be setup correctly to ensure the clock does not go backwards.

Field Summary

Fields

Modifier and Type	Field and Description
static int	EPOCH_BITS Number of bits used for the timestamp giving 69 years from timestampOffsetMs().
static int	MAX_NODE_ID_AND_SEQUENCE_BITS Total number of bits used to represent the distributed node and the sequence within a millisecond.
static int	NODE_ID_BITS_DEFAULT Default number of bits used to represent the distributed node or application which is 10 bits allowing for 1024 nodes (0-1023).
static int	SEQUENCE_BITS_DEFAULT Default number of bits used to represent the sequence within a millisecond which is 12 bits supporting 4,096,000 ids per-second per-node.
static int	UNUSED_BITS High order 2's compliment bit which is unused.

Constructor Summary

Constructors

Constructor and Description
SnowflakeIdGenerator(int nodeIdBits, int sequenceBits, long nodeId, long timestampOffsetMs, EpochClock clock) Construct a new Snowflake id generator for a given node with a provided offset and EpochClock.
SnowflakeIdGenerator(long nodeId) Construct a new Snowflake id generator for a given node with a 0 offset from 1 Jan 1970 UTC and use SystemEpochClock.INSTANCE with NODE_ID_BITS_DEFAULT node ID bits and SEQUENCE_BITS_DEFAULT sequence bits.

Method Summary

Modifier and Type	Method and Description
long	maxNodeId() The max node identity value possible given the configured number of node ID bits.
long	maxSequence() The max sequence value possible given the configured number of sequence bits.
long	nextId() Generate the next id in sequence.
long	nodeId() Node identity which scopes the id generation.
long	timestampOffsetMs() Offset in milliseconds from Epoch of 1 Jan 1970 UTC which is subtracted to give 69 years of ids.

Methods inherited from class java.lang.Object

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

Field Detail

UNUSED_BITS

public static final int UNUSED_BITS

High order 2's compliment bit which is unused.

See Also:

Constant Field Values

EPOCH_BITS

public static final int EPOCH_BITS

Number of bits used for the timestamp giving 69 years from timestampOffsetMs().

See Also:

Constant Field Values

MAX_NODE_ID_AND_SEQUENCE_BITS

public static final int MAX_NODE_ID_AND_SEQUENCE_BITS

Total number of bits used to represent the distributed node and the sequence within a millisecond.

See Also:

Constant Field Values

NODE_ID_BITS_DEFAULT

public static final int NODE_ID_BITS_DEFAULT

Default number of bits used to represent the distributed node or application which is 10 bits allowing for 1024 nodes (0-1023).

See Also:

Constant Field Values

SEQUENCE_BITS_DEFAULT

public static final int SEQUENCE_BITS_DEFAULT

Default number of bits used to represent the sequence within a millisecond which is 12 bits supporting 4,096,000 ids per-second per-node.

See Also:

Constant Field Values

Constructor Detail

SnowflakeIdGenerator

public SnowflakeIdGenerator(int nodeIdBits,
                            int sequenceBits,
                            long nodeId,
                            long timestampOffsetMs,
                            EpochClock clock)

Construct a new Snowflake id generator for a given node with a provided offset and EpochClock.

Parameters:

nodeIdBits - number of bits used to represent the distributed node or application.

sequenceBits - number of bits used to represent the sequence within a millisecond.

nodeId - for the node generating ids.

timestampOffsetMs - to adjust the base offset from 1 Jan 1970 UTC to extend the 69-year range.

clock - to provide timestamps.

SnowflakeIdGenerator

public SnowflakeIdGenerator(long nodeId)

Construct a new Snowflake id generator for a given node with a 0 offset from 1 Jan 1970 UTC and use SystemEpochClock.INSTANCE with NODE_ID_BITS_DEFAULT node ID bits and SEQUENCE_BITS_DEFAULT sequence bits.

Parameters:

nodeId - for the node generating ids.

Method Detail

nodeId

public long nodeId()

Node identity which scopes the id generation. This is limited to maxNodeId().

Returns:

the node identity which scopes the id generation.

timestampOffsetMs

public long timestampOffsetMs()

Offset in milliseconds from Epoch of 1 Jan 1970 UTC which is subtracted to give 69 years of ids.

To offset from 1 Jan 2015 UTC then 1420070400000 can be used.

Returns:

offset in milliseconds from Epoch of 1 Jan 1970 UTC which is subtracted to give 69 years of ids.

maxNodeId

public long maxNodeId()

The max node identity value possible given the configured number of node ID bits.

Returns:

max node identity value.

maxSequence

public long maxSequence()

The max sequence value possible given the configured number of sequence bits.

Returns:

max sequence value.

nextId

public long nextId()

Generate the next id in sequence. If maxSequence() is reached within the same millisecond then this implementation will busy spin until the next millisecond using ThreadHints.onSpinWait() and checking for Thread.isInterrupted().

Specified by:

nextId in interface IdGenerator

Returns:

the next unique id for this node.