[SERVER-15279] Disable hash-based index intersection (AND_HASH) by default Created: 16/Sep/14  Updated: 28/Dec/17  Resolved: 17/Sep/14

Status: Closed
Project: Core Server
Component/s: Querying
Affects Version/s: None
Fix Version/s: 2.6.5, 2.7.7

Type: Task Priority: Major - P3
Reporter: David Storch Assignee: David Storch
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Depends
Related
is related to SERVER-14961 Plan ranker favors intersection plans... Closed
is related to SERVER-15985 plan change in 2.6.5 causes query to ... Closed
Tested
Backport Completed:
Participants:
Case:

 Description   

Performance testing has suggested that hash-based index intersection, implemented by the AND_HASH query execution stage, does not offer a significant performance advantage for test workloads. This is due in part to SERVER-12923, which describes how query optimization can suffer for plans that are not fully pipelined.

Based on the results of this testing, we should disable hash-based intersection by default. It will be possible to re-enable AND_HASH at run time via:

db.adminCommand({setParameter: 1, internalQueryPlannerEnableHashIntersection: 1});

Sort-based intersection will be on by default and will not be affected by this change.



 Comments   
Comment by Githook User [ 17/Sep/14 ]

Author:

{u'username': u'dstorch', u'name': u'David Storch', u'email': u'david.storch@10gen.com'}

Message: SERVER-15279 disable hash-based index intersection by default

(cherry picked from commit 5e2b3c29b438f936eeb0a675e70e0131ab4c145a)

Conflicts:
src/mongo/dbtests/plan_ranking.cpp
Branch: v2.6
https://github.com/mongodb/mongo/commit/775777b99c575edff05262140fbd529316aee939

Comment by Githook User [ 17/Sep/14 ]

Author:

{u'username': u'dstorch', u'name': u'David Storch', u'email': u'david.storch@10gen.com'}

Message: SERVER-15279 disable hash-based index intersection by default
Branch: master
https://github.com/mongodb/mongo/commit/8baf068f5c7bcb52c7cc19bd6343fc2569cd92fc

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