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docs: mention output_rows_skew on partitioned operators in explain-usage #26048

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gabotechs merged 1 commit into from
Oct 5, 2026
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docs: mention output_rows_skew on partitioned operators in explain-usage #26048

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6 changes: 6 additions & 0 deletions docs/source/user-guide/explain-usage.md
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Expand Up @@ -243,6 +243,12 @@ When predicate pushdown is enabled, `DataSourceExec` with `ParquetSource` gains
- `row_pushdown_eval_time`: time spent evaluating row-level filters
- `page_index_eval_time`: time required to evaluate the page index filters

`output_rows_skew` is also reported by operators that execute in multiple
partitions: `RepartitionExec`, `HashJoinExec`, `AggregateExec`,
`BoundedWindowAggExec` and `WindowAggExec`. It shows how evenly their output
rows are spread across partitions, which helps spot data skew (for example, a
hot join or grouping key). With a single partition the skew is always `0%`.

## Postgres-style `EXPLAIN (...)` options

In addition to the legacy keyword form (`EXPLAIN ANALYZE VERBOSE FORMAT tree SELECT ...`),
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