sqlplan-comparelisted

# SQL Server Execution Plan Comparison Skill ## Purpose Identify what changed between two execution plans for the same query — one known-good (baseline) and one regressed (new). Produce a side-by-side diff that explains why the query is slower and what to fix. Applies 20 regression checks (C1–C20). ## Input Accept any of: - Two `.sqlplan` file paths: `baseline.sqlplan` and `new.sqlplan` - Two blocks of raw `.sqlplan` XML pasted inline, labeled Baseline and New - A description of both plans if XML is not available ## How to Run 1. Parse both plans independently 2. Extract the comparison metrics listed below for each plan 3. Produce a side-by-side diff table, then a findings section for every significant change 4. Conclude with a prioritized fix list --- ## Metrics to Compare ### Statement-Level | Metric | Where to Find | Signal | |--------|--------------|--------| | StatementSubTreeCost | `StmtSimple/@StatementSubTreeCost` | > 2× increase = regression | | DegreeOfParallelism | `QueryPlan/@DegreeOfParallelism` | DOP drop = serial plan forced | | GrantedMemory (KB) | `MemoryGrantInfo/@GrantedMemory` | > 2× increase = cardinality inflation | | MaxUsedMemory (KB) | `MemoryGrantInfo/@MaxUsedMemory` | Used > Granted = spill | | CardinalityEstimationModelVersion | `QueryPlan/@CardinalityEstimationModelVersion` | Version drop = compat level change | | CompileCPU (ms) | `StmtSimple/@CompileCPU` | > 2× increase = optimizer struggling | | MissingIndexGroup count | `<MissingInde