ulrichurriola-parada-ops opened a new pull request, #24271:
URL: https://github.com/apache/datafusion/pull/24271
## Which issue does this PR close?
- Closes #.
## Rationale for this change
HashJoinExec's elapsed_compute metric (as reported by EXPLAIN ANALYZE and
ExecutionPlanMetricsSet) includes time spent executing the entire build-side
subtree, not just the join's own work. Any tool that sums elapsed_compute
across a physical plan to estimate total CPU time (e.g. to build a
cost/telemetry model) will double-count that subtree's compute: once under the
child operator(s) that did the work, and again under HashJoinExec.
## What changes are included in this PR?
build_time was previously timed around the entire collect_left_input future
(via left_fut.get_shared(cx) in collect_build_side). That future both drains
the build-side child's stream and builds the hash table, so the child's own
compute got billed to build_time whenever the driving partition executed both
phases inline.
- Scoped the build_time timer inside collect_left_input to start only
after the build-side stream has been fully folded, covering just the
synchronous bounds/hash-map construction.
- Removed the now-redundant wrapping timer in collect_build_side.
## Are these changes tested?
Covered by the existing hash_join test suite (correctness of join output and
other metrics is unaffected). No new test was added to assert the exact
build_time/elapsed_compute value, since there isn't currently a way to
attribute deterministic wall-clock cost to a specific subtree in a unit test.
## Are there any user-facing changes?
elapsed_compute reported for HashJoinExec (e.g. via EXPLAIN ANALYZE) will be
smaller and more accurate, reflecting only the join's own compute rather than
including its build-side subtree. No public API changes.
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