How Efficient is Mongo DB ISOLATION

Question

I came across a document that Mongo DB maintains a global write lock, wanted to know how efficient it is to support "ISOLATION" of "ACID" as of SQL database.

Answer 1

I came across a document that Mongo DB maintains a global write lock

That's old information, MongoDB is now on a database level lock, maybe sometime in the future collection, however, that has been put back in favour of concurrency.

wanted to know how efficient it is to support "ISOLATION" of "ACID" as of SQL database.

First thing first, MongoDB IS NOT AN ACID DATABASE. If you want ACID you should go with an ACID compliant database. Don't try and make a database do what it isn't designed to do.

As for actual isolation, currently MongoDB has isolation on a single document level with atomic operations such as $inc, $set, $unset and all those others. Isolation does not occur on multiple documents, there is an $isolated ( http://docs.mongodb.org/manual/reference/operator/isolated/ ) operator but it is highly recommened not to use it, plus it isn't supported on sharded collections.

There is also a documentation page on providing isolation levels: http://docs.mongodb.org/manual/tutorial/isolate-sequence-of-operations/ but only findAndModify and indexing can provide some element of isolation whereby other queries will not interferer.

Fundamentally, even if it had atomic operations on multiple documents, MongoDB cannot normally support isolation across many documents, this is due to one of its main concurrency features, the ability to subside out of memory operations for ones in memory.

And so I come back to my original point, if you want ACID go to a ACID tech.