feat: add coverage threshold to skip Comet for low-coverage queries#3816
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andygrove wants to merge 3 commits intoapache:mainfrom
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feat: add coverage threshold to skip Comet for low-coverage queries#3816andygrove wants to merge 3 commits intoapache:mainfrom
andygrove wants to merge 3 commits intoapache:mainfrom
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Add spark.comet.exec.coverageThreshold config (0.0-1.0, default 0.0) that reverts to the original Spark plan when the fraction of converted operators falls below the threshold. This avoids the overhead of Spark-to-Comet transitions for queries where only a small percentage of operators can run natively.
Extract classifyNode() to eliminate duplicated match logic between generateTreeString and collectStats. Replace coveragePercent with coverageFraction (0.0-1.0) to match the threshold config units and avoid unnecessary multiply/divide conversions.
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Which issue does this PR close?
Part of #833
Rationale for this change
When Comet can only convert a small fraction of a query's operators, the overhead from Spark-to-Comet transitions can outweigh the benefit of native execution. This adds a simple cost-based mechanism to skip Comet entirely for such queries.
What changes are included in this PR?
spark.comet.exec.coverageThresholdconfig (double, 0.0–1.0, default 0.0 = disabled). When set, Comet falls back to the original Spark plan if the percentage of converted operators is below the threshold.CometCoverageStats.fromPlan()to compute coverage stats from aSparkPlanwithout building the explain string, reusable by both the explain output and the threshold check.CometExecRule._apply()that logs a warning and returns the original plan when coverage is insufficient.How are these changes tested?
Default behavior is unchanged (threshold = 0.0 disables the check). Manual verification that compile succeeds. Tests to be added.