CODEWITHSUNDEEP
mongodblockingdistributed
bettlebrox
bettlebrox

Reputation: 228

Reuse mongo internal distributed locks

I need an distributed lock implementation for my application. I have a number of independent worker processes and I need to enforce a restriction that they can only work on a single account at one time.

The application is writen in c# with a mongo db layer. I noticed that mongo's cluster balancer uses a distributed lock mechanism to control which mongos is doing the balancing and I was wondering if I could reuse the same mechanism in my app?

I'd rather not have the overhead of implementing my own distributed lock mechanism and since all the worker processes alreading interface with mongo so it would be great if I could reuse their implementation.

Upvotes: 4

Views: 1872

Answers (1)

Stennie
Stennie

Reputation: 65373

There is no inherent document-level locking or distributed lock driver API in MongoDB.

MongoDB's internal locks for sharding splits & migrations use a two phase commit pattern against the shard cluster's config servers. You could implement a similar pattern yourself, and there is an example in the MongoDB documentation: Perform Two Phase Commits.

This is likely overkill if you just need a semaphore to prevent workers simultaneously updating the same account document. A more straightforward approach would be to add an advisory lock field (or embedded doc) to your account document to indicate the worker process that is currently using the document. The lock could be set when the worker starts and removed when it finishes. You probably want the lock information to include both a worker process ID and timestamp, so stale locks can be found & removed.

Note that any approach requires coordination amongst your worker processes to check and respect your locking implementation.

Upvotes: 5

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