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Question

I'm developing an application in rails 3.2 with mongodb as database. I am using the mongoid gem.

I want to track all the changes to the database during runtime, but I have no idea how to do it.
Any clues on this?

Answer 1

There are several approaches you could use to track changes to your data, depending on whether you are just interested in monitoring current activity or need to create some sort of transactional history.

In rough order of least-to-most effort:

1) Enable the MongoDB Query Profiler

If you enable the query profiler at a level of " 2 " it will collect profiling data for all operations (reads as well as writes) to a specific database. You can also enable this in your configuration options ) to change the profiling default for all databases on mongod startup. The profile data is saved in a capped collection per database and will only contain a recent snapshot of queries. Query profiling status can also be changed at runtime, so you can easily enable or disable as required.

2) Add Mongoid callbacks to your application

Add appropriate logic Mongoid callbacks such as after_insert , after_save , after_upsert depending on what information you are trying to capture.

3) Create a tailable cursor on the MongoDB oplog

If you run MongoDB as part of a replica set (or with the --replSet option), it creates a capped collection called the oplog (operations log) . You can use a tailable cursor to follow changes as they are committed to the oplog . The oplog details all changes to the database, and is the mechanism MongoDB uses for replication.

Answer 2

I am not familiar with Mongodb nor mongoid , but here is my idea for someone using MySQL (I hope it gives you some clue):

First you take a snapshot of your database (using a tool like mysqldump ).

Then at certain intervals, you check (audit) for those records which have an updated_at value greater (later) than the time you took the snapshot, or your last audit time.

Now, you have two versions of your data, which you can check for changes.

As I said, this is just an idea, and it needs to be more refined. I hope it gives you a clue.