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# Metrics

DataFusion operators expose runtime metrics so you can understand where time is spent and how much data flows through the pipeline. See more in [EXPLAIN ANALYZE](sql/explain.md#explain-analyze).

## Common Metrics

### BaselineMetrics

`BaselineMetrics` are available in most physical operators to capture common measurements.

| Metric          | Description                                                                                                                                                                                        |
| --------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| elapsed_compute | CPU time the operator actively spends processing work.                                                                                                                                             |
| output_rows     | Total number of rows the operator produces.                                                                                                                                                        |
| output_bytes    | Memory usage of all output batches. Note: This value may be overestimated. If multiple output `RecordBatch` instances share underlying memory buffers, their sizes will be counted multiple times. |
| output_batches  | Total number of output batches the operator produces.                                                                                                                                              |

## Operator-specific Metrics

### FilterExec

| Metric      | Description                                                       |
| ----------- | ----------------------------------------------------------------- |
| selectivity | Selectivity of the filter, calculated as output_rows / input_rows |

## TODO

Add metrics for the remaining operators