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I'm working on a game prototype and worried about the following case: Browser does AJAX to Node.JS, which has to do several MongoDB operations using async.series.

What prevents multiple requests at the same time causing the database issues? New events (i.e. db operations) seem like they could be run out of order or in between the async.series steps.

In other words, what happens if a user does AJAX calls very quickly, before the prior ones have finished their async.series. Hopefully that makes sense.

If this is indeed an issue, what is the proper way to handle it?

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  • Node.js is syncronized, it will process only one request at a time. Commented May 26, 2014 at 21:10
  • Thanks, but I am worried that if I have 2 (for example) database events going that a new request may put events in between those. Commented May 26, 2014 at 21:36

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First and foremost, @fmodos's comment should be completely disregarded. It is wrong on many levels but most simply you could have any number of nodes running (say on Heroku) and there is no guarantee that subsequent requests will hit the same node.

Now, I'm going to answer your question by asking more questions. (You really didn't give me a choice here)

What are these operations doing? Inserting documents? Updating existing documents? Removing documents? This is very important because if all you're doing is simply inserting documents then why does it matter if one finishes for before the other? If you're updating documents then you should NOT be issuing a find, grabbing a ref to the object, and then calling save. (I'm making the assumption you're using mongoose, if you're not, I would) Instead what you should be doing is using built in mongo functions like $inc which properly handle concurrent requests.

http://docs.mongodb.org/manual/reference/operator/update/inc/

Does that help at all? If not, please let me know and I will give it another shot.

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Some operations would be getting documents followed by inserting. So yeah, I am most concerned with new events being run in between. I am using mongoose. So doing the series, I am worried about the data changing in between the get and the insert/update.
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Mongo has database wide read/write locks. It gives preference to writes of the same collection first then fulfills reads. So, if by chance, you have Bill writing to the db and Joe is reading at the same time, Bill's write will execute first while Joe waits until the write is complete and then he is given all the data (including Bill's).

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Thanks, I think atomic functions like findAndModify will do the trick.

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