Bad use-case for mongoDB

[Durga Deep]

Folks,

   Was looking at the following capability in mongodb

• http://docs.mongodb.org/manual/tutorial/expire-data/

    We are planning on using a collection in mongodb to act as a MUTEX - so essentially using an entry in the collection so that four applications (running) on different JVMs not duplicate the effort. Based on this use-case and this capability of mongodb - we can set our TTL on this record to few minutes.

   But again was also looking at the following link - which illustrates how mongodb stores it's data.

• http://blog.mongolab.com/2014/01/how-big-is-your-mongodb/

   Would we end up doing a repairDatabase periodically as  illustrated in the link below ?

• http://docs.mongodb.org/manual/reference/method/db.repairDatabase/
  

   Thank you!.

   D

  

[s.molinari]

Can you please explain what this means more precisely? 

so that four applications (running) on different JVMs not duplicate the effort.

What effort, for example?

Scott 

[Durga Deep Tirunagari]

We're making an entry in one of the collections in our mongodb.

In-order to avoid multiple servers (running on different Virtual Machines) trying to handle the same request from a queue. But once the request is served this record (entry) in the collection will be expired based on TTL.

Coming back to my question - from the memory allocation model in mongodb I see that this type of use case can cause the file system to fill up ?

_D

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_Durga Deep

[s.molinari]

Is the queue supposed to be the Mongo collection itself? If so, you might want to think about using a capped collection. It is better made for queueing data. You'd just need to make sure the collection is big enough in size, so that the oldest document never gets deleted/ pushed out of the collection/ queue, before it was "worked" on by one of the JVMs.  

Also, as far as I know, Mongo reuses space available from deleted documents in a TTL scenario. So you shouldn't see an issue with space. What you might have an issue with is de-fragmentation of the data and thus a possible issue with performance. This is why the capped collection might also be a better choice for you. The data stays in a "serial" format and thus is highly performant.

Scott  

[Durga Deep Tirunagari]

Sorry for the delay - 

This is the exactly what we were looking for thanks a million!

_D

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_Durga Deep