[SERVER-63310] Introduce a runtime configurable query knob to disable $group SBE pushdown Created: 04/Feb/22  Updated: 12/Apr/22  Resolved: 12/Apr/22

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

Type: Task Priority: Major - P3
Reporter: Ethan Zhang (Inactive) Assignee: Mihai Andrei
Resolution: Duplicate Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Depends
depends on SERVER-65338 Introduce a runtime configurable quer... Closed
Related
related to SERVER-63283 Add query knob to guard HJ plans for ... Closed
Sprint: QE 2022-04-04, QE 2022-03-07, QE 2022-03-21, QE 2022-04-18
Participants:

 Description   

For newly released SBE features, we still kept the feature flags for them. Those feature flags can only be set at startup time and are seldomly used. When customers run into issues with a new feature, the only choice for them to get a quick workaround without downtime is to disable the whole SBE engine via the internalQueryForceClassicEngine query knob. We should convert those startup-time-only feature flags to runtime-tunable query knobs so customers can disable only a feature, not the entire engine.

joe.sack steve.la Currently, feature flags are created for almost all the projects and they are designed to be startup-time-tunable only. I wonder if we can just change the feature flag to be all runtime-tunable so this works perfectly with our existing process and don't require an extra policy.



 Comments   
Comment by Ethan Zhang (Inactive) [ 04/Feb/22 ]

Based on the design doc linked in this Jira ticket:
Feature flags should generally be settable at server startup only. This supports the use of feature flags as a release/development tool and should not impose an unnecessary burden on server administration.
Also, christopher.harris mentioned that, in Atlas, any parameter change even dynamic is done via a restart to make sure it is persistent. So having this query knob will not benefit Atlas users in terms of saving downtime. But it will help the on-prem customers.

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