Sequential Guid in Java

Question

Considering the post I've made about the sequential guid performance on Microsoft.NET framework (see What are the performance improvement of Sequential Guid over standard Guid?) does somebody have a proper, sure, fast and well working Java implementation of the same algorithm implemented in the Windows DLLs?

Regards Massimo

Answer 1

See this article: http://www.informit.com/articles/article.aspx?p=25862&seqNum=7 (linked to Page 7).

It contains an algorithm for what the author refers to as "COMB" Guids; I reproduce his code (SQL) below:

SET @aGuid = CAST(CAST(NEWID() AS BINARY(10)) 
+ CAST(GETDATE() AS BINARY(6)) AS UNIQUEIDENTIFIER)

Trivial to convert this to Java, or your desired language. The obvious underlying principle is to make the date a component of the Guid. The entire article is a good read, as he does a nice analysis of the performance of the various approaches.

Answer 2

For sequential UUIDs, you are looking for a version 1 UUID. Java UUID Generator project seems to work quite well and is pretty easy to use:

Generators.timeBasedGenerator().generate().toString()

Answer 3

This page links to a couple of version 1 (sequential) UUID implementations in Java: http://johannburkard.de/blog/programming/java/Java-UUID-generators-compared.html

Answer 4

I use this to generate UUIDs (Universally Unique IDs) for my DTOs which act as surrogate keys for transient collections. Don't know if it's the same thing, but it may point you in the right direction.

import java.util.UUID;
...
    private String uuid=null;
...
    protected String getUuid() {
        synchronized (this) {
          if (null ==uuid) {
            uuid = UUID.randomUUID().toString();
          }
          return uuid;
        }
      }