[SERVER-27406] Reduce DocumentSourceCursor batch size from 16MB to 4MB Created: 13/Dec/16  Updated: 05/Apr/17  Resolved: 27/Dec/16

Status: Closed
Project: Core Server
Component/s: Aggregation Framework
Affects Version/s: 3.4.0
Fix Version/s: 3.4.2, 3.5.2

Type: Improvement Priority: Major - P3
Reporter: James Wahlin Assignee: James Wahlin
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Backports
Depends
Related
related to SERVER-27520 Allow unsigned types for MONGO_EXPORT... Closed
Backwards Compatibility: Fully Compatible
Sprint: Query 2017-01-23
Participants:
Linked BF Score: 0

 Description   

DocumentSourceCursor batch size was changed from 4MB to 16MB for MongoDB 3.4 as part of a broader effort to unify user request batch size at 16MB under SERVER-21797. This change led to a mongo-perf performance regression for the "Aggregation.skip" which appears as slower memcpy operations under VTune under DocumentSourceCursor::loadBatch and is likely due to the larger batches exceeding L2/L3 caches.

Testing across our aggregation micro-benchmarks shows a 4MB DocumentSourceCursor batch size restores previous performance across affected tests and does not penalize tests that may benefit from the batching behavior.



 Comments   
Comment by Githook User [ 27/Dec/16 ]

Author:

{u'username': u'jameswahlin', u'name': u'James Wahlin', u'email': u'james.wahlin@10gen.com'}

Message: SERVER-27406 Reduce DocumentSourceCursor batch size from 16MB to 4MB

(cherry picked from commit c76707775edcef041f3a83be2972a739236ef01b)
Branch: v3.4
https://github.com/mongodb/mongo/commit/b01a43cfa073e20503f5a8a3d91c1f2024c6a2a7

Comment by Githook User [ 27/Dec/16 ]

Author:

{u'username': u'jameswahlin', u'name': u'James Wahlin', u'email': u'james.wahlin@10gen.com'}

Message: SERVER-27406 Reduce DocumentSourceCursor batch size from 16MB to 4MB
Branch: master
https://github.com/mongodb/mongo/commit/c76707775edcef041f3a83be2972a739236ef01b

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