determine storageEngine specificity in docs (DOCS-4856)

[DOCS-5139] sections on "multithread replication" and "prefetching indexes" can be updated for new storage engines Created: 31/Mar/15  Updated: 11/Jan/17  Resolved: 06/Jul/15

Status: Closed
Project: Documentation
Component/s: None
Affects Version/s: mongodb-3.0
Fix Version/s: 01112017-cleanup

Type: Sub-task Priority: Major - P3
Reporter: Mark Callaghan Assignee: Kay Kim (Inactive)
Resolution: Done Votes: 0
Labels: storage
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Participants:
Days since reply: 8 years, 32 weeks, 2 days ago

 Description   

In http://docs.mongodb.org/manual/core/replica-set-sync/ a few sections can be updated for new storage engines.

Is this true for all storage engines from the "Multithreaded Replication" section. If it is true then it limits my ability to have long running queries on a replica that isn't getting far behind on replication.

'While applying a batch, MongoDB blocks all reads. As a result, secondaries can never return data that reflects a state that never existed on the primary.'

The "Prefetching Indexes" section is only true for mmapv1, which is explained in the docs for the referenced parameter, secondaryIndexPrefetch, but I think the docs here could be updated.



 Comments   
Comment by Githook User [ 06/Jul/15 ]

Author:

{u'username': u'kay-kim', u'name': u'kay', u'email': u'kay.kim@10gen.com'}

Message: DOCS-5139 update prefetch indexes and multithreaded replication
Branch: master
https://github.com/mongodb/docs/commit/1ddc5e0567bdc1079fba285abceab1e08a5b6b73

Comment by Eric Milkie [ 31/Mar/15 ]

"Pre-Fetching Indexes to Improve Replication Throughput" should be MMAPv1 only.

The Multithreaded Replication section, in the 3.0 and master docs branches, can be changed to something like this:
----------------------------------
MongoDB applies write operations in batches using multiple threads to improve concurrency. MongoDB groups batches by namespace (MMAPv1) or by document id (WiredTiger) and simultaneously applies each group of operations using a different thread. MongoDB always applies write operations to a given document in their original write order.

While applying a batch, MongoDB blocks all read operations. As a result, secondary read queries can never return data that reflect a state that never existed on the primary.

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