[SERVER-79333] [Storage Execution NAMER] Audit v7.0 feature flag Created: 25/Jul/23  Updated: 16/Nov/23  Resolved: 16/Nov/23

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

Type: Task Priority: Major - P3
Reporter: Randolph Tan Assignee: Benety Goh
Resolution: Won't Fix Votes: 0
Labels: former-storex-namer
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Depends
is depended on by SERVER-79330 Audit featureFlag usage in v7.0 branc... Backlog
Issue split
split to SERVER-79590 [Storage Execution EMEA] Audit v7.0 f... Closed
Related
is related to SERVER-79317 Provide more documentation and helper... Closed
Assigned Teams:
Storage Execution
Sprint: Execution Team 2023-11-27
Participants:

 Description   

Intial sync can temporarily reset the fcv value to uninitialized and sets the new value afterwards. This can cause call sites trying to inspect the fcv value to hit this invariant. We need to audit feature flag usage and determine if the feature flag check can be run during initial sync:

If it can never be called when initial sync is running, do nothing. Note that this can be tricky to prove as we once thought the catalog cache loader can never be run while initial sync is happening but it can.

If it might get run during initial sync, this could be the case if the feature is run during initial sync itself, if the feature is in a background thread that runs during initial sync, or if the feature is run in a command that is allowed during initial sync, such as hello, serverStatus, etc. In this case, use one of these options:

  • Use isEnabledUseLastLTSFCVWhenUninitialized. It checks against the last LTS FCV version if the FCV version is unset, but note that this could result in the feature not being turned on even though the FCV will be set to latest once initial sync is complete.
  • Use isEnabledUseLatestFCVWhenUninitialized. This instead checks against the latest FCV version if the FCV version is unset, but note that this could result in the feature being turned on even though the FCV has not been upgraded yet and will be set to lastLTS once initial sync is complete.
  • Write your own special logic to avoid the invariant (for example, waiting for the FCV to become initialized before checking isEnabled, or uasserting instead of invariant-ing)

See this section of the README

gFeatureFlagInternalWritesAreReplicatedTransactionally



 Comments   
Comment by Benety Goh [ 16/Nov/23 ]

The featureFlagInternalWritesAreReplicatedTransactionally affects oplog entry generation on a primary and is not accessed during initial sync. The only reference to this feature flag on 7.0 is in OpObserverImpl::onBatchedWriteComplete() where it is checked using FeatureFlag::isEnabled(). Per guidance laid out in the README, it should be fine to continue using isEnabled.

Comment by Connie Chen [ 01/Aug/23 ]

Moved gFeatureFlagBucketUnpackWithSort, gFeatureFlagShardedTimeSeries, gFeatureFlagColumnstoreIndexes to the Query as these were created by the Query teams (see SERVER-79335)

Generated at Thu Feb 08 06:40:42 UTC 2024 using Jira 9.7.1#970001-sha1:2222b88b221c4928ef0de3161136cc90c8356a66.