Runtime Fuzzing Issue - Affected Parameters

Issue Summary

Parameters requiring special generation logic at startup are not being fuzzed correctly at runtime because RuntimeParametersState.generate_parameters() only calls generate_normal_mongo_parameters(), bypassing the special handling functions.

Root Cause

Startup path:

generate_mongod_parameters()
  → generate_special_mongod_parameters()  (handles 2 params)
  → generate_flow_control_parameters()    (handles 9 params)

Runtime path:

RuntimeParametersState.generate_parameters()
  → generate_normal_mongo_parameters() ONLY

Affected Parameters (11 total)

Special Mongod Parameters (2)

1. throughputProbingReadWriteRatio - fuzz_at: ["startup", "runtime"], period: 5
2. throughputProbingStepMultiple - fuzz_at: ["startup", "runtime"], period: 5

Flow Control Parameters (9)

Note: Only fuzzed at runtime when enableFlowControl=true at startup

1. flowControlTicketAdderConstant - fuzz_at: ["startup", "runtime"], period: 5
2. flowControlDecayConstant - fuzz_at: ["startup", "runtime"], period: 5
3. flowControlFudgeFactor - fuzz_at: ["startup", "runtime"], period: 5
4. flowControlMinTicketsPerSecond - fuzz_at: ["startup", "runtime"], period: 5
5. flowControlSamplePeriod - fuzz_at: ["startup", "runtime"], period: 5
6. flowControlTargetLagSeconds - fuzz_at: ["startup", "runtime"], period: 5
7. flowControlThresholdLagPercentage - fuzz_at: ["startup", "runtime"], period: 5 ⚠️ BROKEN
8. flowControlTicketMultiplierConstant - fuzz_at: ["startup", "runtime"], period: 5
9. flowControlWarnThresholdSeconds - fuzz_at: ["startup", "runtime"], period: 5

Critical Failure

flowControlThresholdLagPercentage will throw an exception at runtime because it tries to call rng.randint(0.0, 1.0) which requires integers, not floats. At startup it correctly uses rng.random().

Related Files

• buildscripts/resmokelib/testing/hooks/fuzz_runtime_parameters.py (line 58)
• buildscripts/resmokelib/generate_fuzz_config/mongo_fuzzer_configs.py (lines 252-346)
• buildscripts/resmokelib/generate_fuzz_config/config_fuzzer_limits.py