id autoincrement/sequence emulation with CassandraDB/MongoDB etc

Question

I'm trying to build small web-system (url shortcutting) using nonsql Cassandra DB, the problem I stack is id auto generation.

Did someone already stack with this problem?

Thanks.

P.S. UUID not works for me, I do need to use ALL numbers from 0 to Long.MAX_VALUE (java). so I do need something that exactly works like sql sequence

UPDATED:

The reason why I'm not ok with GUID ids is inside of scope of my application.

My app has url shortcutting part, and I do need to make url as short as possible. So I follow next approach: I'm taking numbers starting from 0 and convert it base64 string. So in result I have url like mysite.com/QA (where QA is base 64 string).

This is was very easy to implement using SQL DB, I just took auto incremented ID, convert it to URL and was 100-percents sure, that URL is unique.

Answer 1

Don't know about Cassandra, but with mongo you can have an atomic sequence (it won't scale, but will work the way it should, even in sharded environment if the query has the sharded field).

It can be done by using the findandmodify command.

Let's consider we have a special collection named sequences and we want to have a sequence for post numbers (named postid), you could use code similar to this:

> db.runCommand( { "findandmodify" : "sequences",
                   "query" : { "name" : "postid"},
                   "update" : { $inc : { "id" : 1 }},
                   "new" : true } );

This command will return atomically the updated (new) document together with status. The value field contains the returned document if the command completed successfully.