[SERVER-14401] Behaviour of replication, and reading from secondaries Created: 01/Jul/14  Updated: 10/Dec/14  Resolved: 01/Jul/14

Status: Closed
Project: Core Server
Component/s: Replication
Affects Version/s: 2.4.6
Fix Version/s: None

Type: Question Priority: Minor - P4
Reporter: simon Assignee: Unassigned
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Participants:

 Description   

I would like to understand the behaviour of writes as they are replicated across to secondaries to confirm or debunk my understanding.

In our situation we write batches of individual documents in what we call a snapshot, related by a field in each containing the snapshot id. When we have completed writing a batch (20k+) of documents, we 'close' the snapshot by updating an additional snapshot document, which contains meta data about when, by whom, and the state of the snapshot. At that point no more documents can be written into that snapshot. None of the documents that make up the snapshot can be mutated at any point.

Am I correct in thinking that all writes to the primary are replayed in exactly the same order to the secondary, from the oplog. If this statement holds true, I can then assume that once i 'see' that snapshot as 'closed' in the secondary, I can be sure that all the documents have also been replicated to the secondary.



 Comments   
Comment by Thomas Rueckstiess [ 01/Jul/14 ]

Hi Simon,

The SERVER project is for reporting bugs or feature suggestions for the MongoDB server.

For MongoDB-related support discussion please post on the mongodb-users group (http://groups.google.com/group/mongodb-user) or Stack Overflow with the mongodb tag. A question like this involving more discussion would be best posted on the mongodb-users group.

I'm closing this and your previous question, SERVER-14392.

Thanks,
Thomas

Comment by simon [ 01/Jul/14 ]

Kunal pointed me to a video (http://www.mongodb.com/presentations/replication-internals-life-write-0) that explains what I was wanting to understand. Could you please confirm that the 'replaying' of changes are played in order on secondaries in 2.4.6. Thanks, Simon

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