Query Insights: Planner-tree traversal helpers miss shard branches

[tnaum-ms]

Summary

findStageInPlan() in ExplainPlanAnalyzer.ts and collectPlannerStages() in StagePropertyExtractor.ts only traverse inputStage and inputStages — they do not recurse through shards structures. In contrast, traverseStages() (execution-stage traversal for UI) already handles shards.

This means for sharded DocumentDB clusters, planner-stage signals like isBitmap can be missed when they appear under a shard branch. Only Stage 2 informational badges (bitmap, low-cardinality) are affected — Stage 3 (AI) receives the raw explain JSON and is unaffected.

What needs to change

• Extend findStageInPlan() to recurse through shards structures (matching traverseStages() behavior).
• Extend collectPlannerStages() similarly.
• Add a sharded test case where IXSCAN.isBitmap === true appears under a shard branch.

Related

• Query Insights: Improve with Explain Schema #522 — Query Insights: Improve with Explain Schema — should be tackled together, as formalizing the explain schema will inform how shard traversal should be structured.

Origin

Identified during review of PR #616 (R-002 in docs/analysis/pr-616-review.md). Severity: Low.