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docs: add HashJoinExec metrics to user guide #24055

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3 changes: 2 additions & 1 deletion datafusion/physical-plan/src/joins/utils.rs
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Expand Up @@ -1758,6 +1758,7 @@ fn append_probe_indices_in_order(
/// Metrics for build & probe joins
#[derive(Clone, Debug)]
pub(crate) struct BuildProbeJoinMetrics {
// Keep these metric descriptions in sync with docs/source/user-guide/metrics.md.
pub(crate) baseline: BaselineMetrics,
/// Total time for collecting build-side of join
pub(crate) build_time: metrics::Time,
Expand All @@ -1773,7 +1774,7 @@ pub(crate) struct BuildProbeJoinMetrics {
pub(crate) input_batches: metrics::Count,
/// Number of rows consumed by probe-side this operator
pub(crate) input_rows: metrics::Count,
/// Fraction of probe rows that found more than one match
/// Fraction of probe rows that found at least one match
pub(crate) probe_hit_rate: metrics::RatioMetrics,
/// Average number of build matches per matched probe row
pub(crate) avg_fanout: metrics::RatioMetrics,
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19 changes: 19 additions & 0 deletions docs/source/user-guide/metrics.md
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Expand Up @@ -42,6 +42,25 @@ DataFusion operators expose runtime metrics so you can understand where time is
| ----------- | ----------------------------------------------------------------- |
| selectivity | Selectivity of the filter, calculated as output_rows / input_rows |

### HashJoinExec

`HashJoinExec` also exposes the common `BaselineMetrics`. Its
`elapsed_compute` metric is the sum of the build-side collection time and the
probe-side join time.

| Metric | Description |
| ----------------------- | -------------------------------------------------------------------------------------------- |
| build_time | Total time spent collecting and building the build side of the join. |
| build_input_batches | Number of input batches consumed from the build side. |
| build_input_rows | Number of input rows consumed from the build side. |
| build_mem_used | Peak memory used by the build side, in bytes. |
| join_time | Total time spent joining probe-side batches against the build side. |
| input_batches | Number of input batches consumed from the probe side. |
| input_rows | Number of input rows consumed from the probe side. |
| probe_hit_rate | Fraction of probe-side rows that matched at least one build-side row. |
| avg_fanout | Average number of build-side matches per matched probe-side row. |
| array_map_created_count | Number of times `HashJoinExec` created an `ArrayMap` for perfect hash join lookup execution. |

## TODO

Add metrics for the remaining operators