[SERVER-81103] disable mirroredReads in plan_cache_stats_all_hosts_sharded Created: 15/Sep/23  Updated: 29/Oct/23  Resolved: 15/Sep/23

Status: Closed
Project: Core Server
Component/s: None
Affects Version/s: None
Fix Version/s: 7.1.0-rc4

Type: Bug Priority: Major - P3
Reporter: Maddie Zechar Assignee: Maddie Zechar
Resolution: Fixed Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Backports
Depends
Backwards Compatibility: Fully Compatible
Operating System: ALL
Backport Requested:
v7.1
Sprint: QI 2023-09-18
Participants:
Linked BF Score: 8

 Description   

Starting in 4.4, mirrored reads are enabled by default with a sampling rate of 0.10. If not disabled, the primary node mirrors supported reads (this includes find queries) to the secondary node's cache to "warm it up" to reduce performance impact of primary elections. Here the cache means "everything on RAM", which includes the plan cache. Thus even though the primary node executes a find query, the secondary's cache will "mirror" this read and have a plan for it in its plan cache. This results in the secondary having more plans in the cache than it executed. We disable this mirroring so the test passes in burn_in_tests.



 Comments   
Comment by Githook User [ 21/Sep/23 ]

Author:

{'name': 'madelinezec', 'email': 'mez2113@columbia.edu', 'username': 'madelinezec'}

Message: SERVER-81103 disable mirroredReads in plan_cache_stats_all_hosts_sharded
Branch: v7.1
https://github.com/mongodb/mongo/commit/dc03829c2ff899c9f36a6f03dd45ebbce2671020

Comment by Maria Prinus [ 20/Sep/23 ]

Hi maddie.zechar@mongodb.com, there is a request for 7.1 backport, please, note that v7.1 is frozen. Reach out to @server-release-managers in #server-release channel to merge the backport to 7.1

Comment by Liubov Molchanova [ 20/Sep/23 ]

Requesting backport as the issue continues to happen on v7.1 (please, see BFG-2094095)

Comment by Githook User [ 15/Sep/23 ]

Author:

{'name': 'madelinezec', 'email': 'mez2113@columbia.edu', 'username': 'madelinezec'}

Message: SERVER-81103 disable mirroredReads in plan_cache_stats_all_hosts_sharded
Branch: master
https://github.com/mongodb/mongo/commit/627895b8474ae137acffff5d5352ed1318d438b7

Generated at Thu Feb 08 06:45:29 UTC 2024 using Jira 9.7.1#970001-sha1:2222b88b221c4928ef0de3161136cc90c8356a66.