CODEWITHSUNDEEP
mongodbcollections
Сергей Илларионов
Сергей Илларионов

Reputation: 399

Can mongo do autoremove collections?

I heared, that mongo can do it, but I can't find how. Can mongo create collections, which will be autoremove in future, from time, which i can setup? Or Mongo can't do this magic?

Upvotes: 0

Views: 2421

Answers (2)

Markus W Mahlberg
Markus W Mahlberg

Reputation: 20703

Collections are auto created on the first write operation (insert, upsert, index creation). So this magic is covered.

If your removal is based on time, you could use cron or at to run this little script

mongo yourDBserver/yourDB --eval 'db.yourCollection.drop()’

As Sammaye pointed out, creating indices is a costly operation. I would assume there is something wrong with your data model. For semantically distinguishing documents, I'd rather create a field on them which does that and set an expiration date or a creation date and a time frame in which the documents are valid and use TTL indices to remove all of those documents.

For using an expiration date, you have to set a field to an ISODate and create a TTL index without a duration:

db.yourColl.ensureIndex({"yourExpirationDateField":1},{expireAfterSeconds:0})

In the case you want the documents to be valid for let's say a week after they are created, you would use the following:

db.yourColl.ensureIndex({"yourCreationDate":1},{expireAfterSeconds:604800})

Either way, here is what happens: Once every minute a background thread called TTLMonitor wakes up, gets all TTL indices for the server and starts processing them. It scans the TTL index, looking for the date values, adds the value given for "expireAfterSeconds" and deletes all documents which it determined to be invalid by now. This process takes some time, so don't expect the documents to be deleted on the very second they expire.

The big advantage of that approach: you don't need any triggering logic to be maintained, the deletes are done automagically in the background and you don't put any load on your application. Plus, using an expiration date, your have very granular control over when a document expires.

The drawback is ... ... Well, if I want to find one it would be that you have to insert a creation date for every document or calculate and insert an expiration date. And you have to send an administrative command to the mongod/mongos once in the application lifetime...

Upvotes: 0

mabc224
mabc224

Reputation: 742

mongodb cannot auto remove collections but it can auto remove BSON records. You just need to set ttl(Time to live) index on a date field that exists in BSON record . You can read more here MongoDb: Expire Data from Collections by Setting TTL

Upvotes: 1

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