Distributed Unique ID
1. UUID
advantage
* Generate ID performance is very good
* Simple and easy to code
* Unique in the world
shortcoming
* uuid has no order and cannot be guaranteed to increment
* Too long, using string storage, as the primary key to build an index query is inefficient
Second, snowflake snowflake algorithm
18 digits
Algorithm: pass timestamp + machine code + serial code
The database uses bigint only 8 bytes
Code:
public class IdWorker { //protected static final Logger LOG = LoggerFactory.getLogger(IdWorker.class); private long workerId; private long datacenterId; private long sequence = 0L; private long twepoch = 1288834974657L; private long workerIdBits = 5L; private long datacenterIdBits = 5L; private long maxWorkerId = -1L ^ (-1L << workerIdBits); private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits); private long sequenceBits = 12L; private long workerIdShift = sequenceBits; private long datacenterIdShift = sequenceBits + workerIdBits; private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits; private long sequenceMask = -1L ^ (-1L << sequenceBits); private long lastTimestamp = -1L; public IdWorker(long workerId, long datacenterId) { // sanity check for workerId if (workerId > maxWorkerId || workerId < 0) { throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId)); } if (datacenterId > maxDatacenterId || datacenterId < 0) { throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId)); } this.workerId = workerId; this.datacenterId = datacenterId; // LOG.info(String.format("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d", timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId)); } public synchronized long nextId() { long timestamp = timeGen(); if (timestamp < lastTimestamp) { // LOG.error(String.format("clock is moving backwards. Rejecting requests until %d.", lastTimestamp)); throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp)); } if (lastTimestamp == timestamp) { sequence = (sequence + 1) & sequenceMask; if (sequence == 0) { timestamp = tilNextMillis(lastTimestamp); } } else { sequence = 0L; } lastTimestamp = timestamp; return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence; } protected long tilNextMillis(long lastTimestamp) { long timestamp = timeGen(); while (timestamp <= lastTimestamp) { timestamp = timeGen(); } return timestamp; } protected long timeGen() { return System.currentTimeMillis(); } }
transfer
IdWorker idWorker1 = new IdWorker(1,0); for (int i = 0; i < 20; i++) { long id = idWorker1.nextId(); System.out.println(id); }