[SERVER-41560] MongoDB should default the snapshot window size to 0 when running with the WT inMemory storage engine Created: 06/Jun/19  Updated: 29/Oct/23  Resolved: 02/Jul/19

Status: Closed
Project: Core Server
Component/s: Storage
Affects Version/s: None
Fix Version/s: 4.2.0-rc3, 4.3.1

Type: Bug Priority: Major - P3
Reporter: Dianna Hohensee (Inactive) Assignee: Dianna Hohensee (Inactive)
Resolution: Fixed Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Backports
Depends
Related
is related to SERVER-41244 The WT inMemory storage engine needs ... Closed
Backwards Compatibility: Fully Compatible
Operating System: ALL
Backport Requested:
v4.2
Sprint: Execution Team 2019-06-17, Execution Team 2019-07-01, Execution Team 2019-07-15
Participants:
Linked BF Score: 0

 Description   

The WT inMemory storage engine does not need to maintain snapshot history nor does it have a metric which MongoDB can use to gauge cache pressure and control the snapshot history window size. The window size should be kept at 0 for v4.2. inMemory members of a replica set cannot actually run transactions in v4.2, though they can replicate them.

Voting inMemory replica set members require the replica set config to set the writeConcernMajorityJournalDefault to false. Replica sets with such configuration are not currently allowed to run replica set / shared transactions.

An inMemory replica set with writeConcernMajorityJournalDefault set to true must be non-voting. Therefore, such a member cannot be primary. Transactions are only run against primary replica set members. So again, the inMemory node cannot directly run transactions, only replicate them as a secondary.

There is no need for inMemory nodes to maintain snapshot history.



 Comments   
Comment by Githook User [ 09/Jul/19 ]

Author:

{'name': 'Dianna Hohensee', 'username': 'DiannaHohensee', 'email': 'dianna.hohensee@10gen.com'}

Message: SERVER-41560 default the snapshot window size to 0 when running with the WT inMemory storage engine

(cherry picked from commit 164e785735f0fd8db2e0c68b86c2278ddc92a671)
Branch: v4.2
https://github.com/mongodb/mongo/commit/62eb326eb1f2fc7ee874af28b0f5e4aca462d988

Comment by Githook User [ 02/Jul/19 ]

Author:

{'name': 'Dianna Hohensee', 'username': 'DiannaHohensee', 'email': 'dianna.hohensee@10gen.com'}

Message: SERVER-41560 default the snapshot window size to 0 when running with the WT inMemory storage engine
Branch: master
https://github.com/mongodb/mongo/commit/164e785735f0fd8db2e0c68b86c2278ddc92a671

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