Fuzzing failure

[fpetkovski]

https://github.com/thanos-io/promql-engine/actions/runs/23097752531/job/67143083193?pr=694

[fpetkovski]

@claude

[claude]

Claude finished @fpetkovski's task in 12m 49s —— View job

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Investigating Fuzzing Failure

• Gather context: analyzed the codebase structure
• Explore potential failure areas in the engine
• Access actual fuzzing failure logs

Analysis Summary

I've done a thorough review of the codebase but cannot determine the exact failure without seeing the CI logs from the linked run. The three fuzzing tests being run are:

1. FuzzEnginePromQLSmithInstantQuery (90s) — compares Thanos engine vs Prometheus for float instant queries
2. FuzzNativeHistogramQuery (90s) — compares Thanos engine vs Prometheus for native histogram queries
3. FuzzNodesMarshalJSON (30s) — tests JSON serialization roundtrip of logical plan nodes

Key Known Exclusions in validateExpr

The fuzz test currently has these exclusions for known differences:

• sort/sort_desc/sort_by_label/sort_by_label_desc — skipped for native histograms (Prometheus filters out histograms in nested sort)
• predict_linear with StepInvariant(MatrixSelector) — Thanos can't handle this correctly
• timestamp for native histograms — has a TODO comment: // TODO(johrry): Remove after merging https://github.com/thanos-io/promql-engine/pull/598

Blocked: Need CI Logs or PR Details

To fix this, I need one of the following:

Option 1: Paste the relevant failure output from the CI log at:
https://github.com/thanos-io/promql-engine/actions/runs/23097752531/job/67143083193

Option 2: Run gh run view 23097752531 --repo thanos-io/promql-engine --log-failed and share the output

Option 3: Share what PR thanos-io#694 changes (title, description, or diff): gh pr diff 694 --repo thanos-io/promql-engine

The failure output will show the query, load data, and result mismatch (or panic), which is necessary to identify and fix the issue.