nikolas-sapa opened a new pull request, #26246:
URL: https://github.com/apache/datafusion/pull/26246
## Which issue does this PR close?
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- Closes #19045.
- Part of #16602 (add a user-guide page documenting operator metrics).
## Rationale for this change
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Why are you proposing this change? If this is already explained clearly in
the
issue then this section is not needed. Explaining clearly why changes are
proposed helps reviewers understand your changes and offer better
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#16602 asks for a documentation page covering the runtime metrics each
operator
exposes. `FilterExec` (#19043) and `HashJoinExec` are already documented;
`NestedLoopJoinExec` was left as an unchecked item on that list. Without the
page entry, the meaning of the build-probe and spill metrics a nested-loop
join
reports in `EXPLAIN ANALYZE` can only be found by reading the operator
source.
## What changes are included in this PR?
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There is no need to duplicate the description in the issue here but it is
sometimes worth providing a summary of the individual changes in this PR.
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Adds a `NestedLoopJoinExec` section to `docs/source/user-guide/metrics.md`,
in
the same shape as the existing `FilterExec` and `HashJoinExec` sections:
- the shared build-probe metrics (`build_time`, `build_input_batches`,
`build_input_rows`, `build_mem_used`, `join_time`, `input_batches`,
`input_rows`) and the join-level `selectivity` metric
(output_rows / (left_rows * right_rows))
- the spill metrics (`spill_count`, `spilled_bytes`, `spilled_rows`) that the
operator surfaces during memory-limited execution, with a short explanation
of when that mode kicks in
- a note that `selectivity` is a `Summary`-level metric while the other
operator-level metrics are `Dev` metrics
Every description was cross-checked against the source rather than written
from
imagination: the `BuildProbeJoinMetrics` doc comments in
`datafusion/physical-plan/src/joins/utils.rs`, `NestedLoopJoinMetrics` in
`joins/nested_loop_join.rs` (including where `selectivity.add_total` /
`add_part` are updated), `SpillMetrics` in `datafusion-physical-expr-common`,
and `MetricValue::name()` for the `spill_count` field name.
## Are these changes tested?
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Documentation only, no code changes — no new tests needed. Formatting was
verified with `./ci/scripts/doc_prettier_check.sh` (clean).
## Are there any user-facing changes?
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If there are user-facing changes then we may require documentation to be
updated before approving the PR. If there are any breaking changes to public
APIs, please add the `api change` label.
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User-facing documentation only: the metrics user-guide page now documents
`NestedLoopJoinExec` metrics. No API or behavior changes.
## AI assistance disclosure
This PR was prepared with the assistance of an AI coding agent. Per the
[AI policy](https://datafusion.apache.org/contributor-guide/ai-policy.html):
I have personally read the entire diff above, verified every metric name and
description against the operator source listed in "What changes are
included",
and I understand the selection (build-probe metrics shared via
`BuildProbeJoinMetrics`, the Summary-level `selectivity` ratio recorded in
`NestedLoopJoinMetrics`, and `SpillMetrics` during memory-limited execution)
end-to-end. I am happy to respond to review comments myself and to adjust any
wording the reviewers prefer.
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