c#生成唯一编号方法记录，可用数据库主键 唯一+有序

数据库主键目前主要有两种：

a、自增数值型

　　优：占用空间小，插入快，有序对索引友好，易懂

缺：多数据库迁移会有重复键值问题，有可能爆表

b、GUID

　　优：多数据库唯一

　　缺：占用空间大，无序对索引不友好，不易懂

察看GUD发现最主要的问题还是在于无序对索引不友好，会引起性能问题，已知有以下两种方式可以解决：

1、基于Twitter的snowflake算法，生成一个long型ID，参考代码如下：

public class IdWorker
{
    private long workerId;
    private long datacenterId;
    private long sequence = 0L;

    private static long twepoch = 1288834974657L;

    private static long workerIdBits = 5L;
    private static long datacenterIdBits = 5L;
    private static long maxWorkerId = -1L ^ (-1L << (int)workerIdBits);
    private static long maxDatacenterId = -1L ^ (-1L << (int)datacenterIdBits);
    private static long sequenceBits = 12L;

    private long workerIdShift = sequenceBits;
    private long datacenterIdShift = sequenceBits + workerIdBits;
    private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private long sequenceMask = -1L ^ (-1L << (int)sequenceBits);

    private long lastTimestamp = -1L;
    private static object syncRoot = new object();

    public IdWorker(long workerId, long datacenterId)
    {

        // sanity check for workerId
        if (workerId > maxWorkerId || workerId < 0)
        {
            throw new ArgumentException(string.Format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0)
        {
            throw new ArgumentException(string.Format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public long nextId()
    {
        lock (syncRoot)
        {
            long timestamp = timeGen();

            if (timestamp < lastTimestamp)
            {
                throw new ApplicationException(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) << (int)timestampLeftShift) | (datacenterId << (int)datacenterIdShift) | (workerId << (int)workerIdShift) | sequence;
        }
    }

    protected long tilNextMillis(long lastTimestamp)
    {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp)
        {
            timestamp = timeGen();
        }
        return timestamp;
    }

    protected long timeGen()
    {
        return (long)(DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalMilliseconds;
    }
}

2、用NewId开源项目

　　项目地址：https://github.com/phatboyg/NewId

使用方法：

NewId id = NewId.Next(); //produces an id like {11790000-cf25-b808-dc58-08d367322210}

// Supports operations similar to GUID
NewId id = NewId.Next().ToString("D").ToUpperInvariant();
// Produces 11790000-CF25-B808-2365-08D36732603A

// Start from an id
NewId id = new NewId("11790000-cf25-b808-dc58-08d367322210");

// Start with a byte-array
var bytes = new byte[] { 16, 23, 54, 74, 21, 14, 75, 32, 44, 41, 31, 10, 11, 12, 86, 42 };
NewId theId = new NewId(bytes);