[EXPLAIN] remove cross join from EXPLAIN ANALYZE #33613
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ggevay
approved these changes
Sep 18, 2025
| ]); | ||
| from.extend(["JOIN mz_introspection.mz_dataflow_global_ids mdgi ON (mlm.global_id = mdgi.global_id)", | ||
| "LEFT JOIN mz_introspection.mz_expected_group_size_advice megsa ON (megsa.dataflow_id = mdgi.id AND mlm.operator_id_start <= megsa.region_id AND megsa.region_id < mlm.operator_id_end)"]); | ||
| "LEFT JOIN (generate_series((mlm.operator_id_start) :: int8, (mlm.operator_id_end - 1) :: int8) AS valid_id JOIN \ |
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I'm wondering if this generate_series could be on the left side of the left join. Having it on the right side means that the right side is correlated with the left side, which is a complicated left join lowering case, with its own code path.
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I started with it on the left side, but I got redundant rows. (There may be a good way to hide those, but my SQL skill wasn't sufficient to the task.) The resulting plan is not small, but there is no cross join...
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I'm going to merge after a tiny doc update, but I made https://github.com/MaterializeInc/database-issues/issues/9730 to record your idea.
mgree
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The range query in operator IDs was leading to a cross join with a filter; using
generate_serieswe can get a proper equijoin.Motivation
https://github.com/MaterializeInc/database-issues/issues/9658
Checklist
$T ⇔ Proto$Tmapping (possibly in a backwards-incompatible way), then it is tagged with aT-protolabel.