Memory-Mapped Storage Engine

From MongoDb's site, the current only support storage engine is Memory-Mapped Storage Engine. I am wondering how it supports atomicity in the presence of system crash(i.e power failure)? Does it depend on the OS? Is there any reference about this topic?

What开发者_如何学Python are the pros and cons of this design comparing with:

1. couchdb's crash only design which depends on append only b+tree.
2. sqlite's rollback journal file

Thanks

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This is the page you are looking for:

http://www.mongodb.org/display/DOCS/Durability+and+Repair

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Either you use a replica set for ensure that the data arrived on at least N replica nodes or for the standalone case you'll wait for MongoDB 1.8 having a dedicated journal to ensure better durability across crashes (should be available with the latest 1.7.X unstable release). And apart from that: Google - this issue has been discussed and documented in depth in various postings and blogs. Not sure why don#t research first yourself.