Summary

Setting cluster parameter fleCompactionOptions in a mixed binary sharded cluster (config server on v8.0, one or more shards on v7.0) can cause the setClusterParameter command to never complete when the parameter value includes an unknown field. The config server accepts the parameter, but shards running v7.0 reject it and the coordinator retries indefinitely.

Background

The FLECompactionOptions IDL definition changed its strictness between versions:

• In v7.0, FLECompactionOptions is strict:true, so extra/unknown fields cause validation to fail.
• In v8.0, FLECompactionOptions was changed to strict:false as part of SERVER-85747, so unknown fields are silently accepted.

setClusterParameter is coordinated by the config server:

1. The config server parses and validates the request.
2. A SetClusterParameterCoordinator is instantiated and propagates the setClusterParameter command to all shards.
3. On failure, the coordinator retries the operation until it succeeds.