[SERVER-22624] Why the journal is unnecessary for WiredTiger Created: 16/Feb/16  Updated: 17/Feb/16  Resolved: 17/Feb/16

Status: Closed
Project: Core Server
Component/s: WiredTiger
Affects Version/s: None
Fix Version/s: None

Type: Question Priority: Trivial - P5
Reporter: Nilap Shah Assignee: Unassigned
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified
Environment:

MongoDB 3.0


Participants:

 Description   

I just want to know
Why the journal is unnecessary for WiredTiger



 Comments   
Comment by Ramon Fernandez Marina [ 17/Feb/16 ]

nilap.shah@gmail.com, please note that the SERVER project is for reporting bugs or feature suggestions for the MongoDB server. For MongoDB-related support discussion please post on the mongodb-user group or Stack Overflow with the mongodb tag, where your question will reach a larger audience. A question like this involving more discussion would be best posted on the mongodb-user group. See also our Technical Support page for additional support resources.

Regards,
Ramón.

Comment by Alexander Gorrod [ 16/Feb/16 ]

WiredTiger uses a protocol called MVCC, which means that we never overwrite data on disk. This allowed us to implement a mechanism called checkpointing that saves the state of a database at a particular point in time. Those checkpoints provide consistent durability guarantees similar to journaling.

The difference between checkpointing and journaling is that it is much more expensive to create a checkpoint than it is to journal an operation. Which means checkpointing isn't a practical solution for applications that need to guarantee that updates are durable (i.e: available after a crash) soon after they are submitted.

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