如何设置MySQL分布式架构主键ID，为什么不能使用自增ID或者UUID做主键？
public class SnowflakeIdGenerator {
// 起始的时间戳
private static final long START_STAMP = 1480166465631L;
// 每一部分占用的位数
private static final long SEQUENCE_BIT = 12;
private static final long MACHINE_BIT = 10;
private static final long TIMESTAMP_BIT = 41;
// 每一部分的最大值
private static final long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
private static final long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
// 每一部分向左的位移
private static final long MACHINE_LEFT = SEQUENCE_BIT;
private static final long TIMESTAMP_LEFT = SEQUENCE_BIT + MACHINE_BIT;
private long machineId;
private long sequence = 0L;
private long lastStamp = -1L;
public SnowflakeIdGenerator(long machineId) {
if (machineId > MAX_MACHINE_NUM || machineId < 0) {
throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
}
this.machineId = machineId;
}
public synchronized long nextId() {
long currStamp = getNewStamp();
if (currStamp < lastStamp) {
throw new RuntimeException("Clock moved backwards. Refusing to generate id");
}
if (currStamp == lastStamp) {
sequence = (sequence + 1) & MAX_SEQUENCE;
if (sequence == 0L) {
currStamp = getNextStamp(lastStamp);
}
} else {
sequence = 0L;
}
lastStamp = currStamp;
return (currStamp - START_STAMP) << TIMESTAMP_LEFT
| machineId << MACHINE_LEFT
| sequence;
}
private long getNextStamp(long lastStamp) {
long stamp = getNewStamp();
while (stamp <= lastStamp) {
stamp = getNewStamp();
}
return stamp;
}
private long getNewStamp() {
return System.currentTimeMillis();
}
}