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MongoDB and Auto Increment

Chris Shiflett shares a solution to emulate the MySQL auto_increment with MongoDB. While you should read his post, the proposed solution is:

db.seq.findAndModify({    
    query: {"_id":"users"},   
     update: {$inc: {"seq":1}},   
     new: true
});

☞ shiflett.org

Kenny Gorman warns that the above solution is not exactly optimal:

When using this technique each insert would require both the insert as well as the findAndModify command which is a query plus an update. So now you have to perform 3 operations where it used to be one. Not only that, but there are 3 more logical I/O’s due to the query, and those might be physical I/O’s. This pattern is easily seen with the mongostat utility.

☞ www.kennygorman.com

I remember Twitter has tried to solve a similar problem — probably at a different, larger scale — and they came up with Snowflake:

We needed something that could generate tens of thousands of ids per second in a highly available manner. This naturally led us to choose an uncoordinated approach. These ids need to be roughly sortable, meaning that if tweets A and B are posted around the same time, they should have ids in close proximity to one another since this is how we and most Twitter clients sort tweets.

☞ engineering.twitter.com

If you have other ideas (even if not directly related to MongoDB) I’d love to hear them!

Original title and link for this post: MongoDB and Auto Increment (published on the NoSQL blog: myNoSQL)