Remove costing index scan of hypertable parent #7768
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mkindahl
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When computing cost for a merge join path, an index scan will be done on the relation to find the actual variable range using `get_actual_variable_range()`, which will include an index scan of the hypertable parent. In addition to being unneccessary, it can also cause problems in situations where the hypertable parent contains data as a result of a bug. There is a check that an index scan is not done for a partitioned table, so we do the same here by setting the indexlist to NIL after hypertable expansion. The index list is needed while expanding the hypertables to construct correct index scans for chunks of a hypertable.
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Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## main #7768 +/- ##
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+ Coverage 80.06% 81.89% +1.82%
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Files 190 247 +57
Lines 37181 45432 +8251
Branches 9450 11356 +1906
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+ Hits 29770 37205 +7435
- Misses 2997 3749 +752
- Partials 4414 4478 +64 ☔ View full report in Codecov by Sentry. |
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@akuzm, @gayyappan: please review this pull request.
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| /* | ||
| * Set the indexlist for a hypertable parent to NIL since we | ||
| * should not try to do any index scans on hypertable parents, | ||
| * similar to how it works for partitioned tables. |
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Is this something that Postgres does for partitioned tables?? If yes then would be good to point to the postgres source code here.
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It is done inside get_actual_variable_range, which is mentioned last in the paragraph.
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... well, later in the paragraph, not last.
fabriziomello
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Feb 25, 2025
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When computing cost for a merge join path, an index scan will be done on the relation to find the actual variable range using
get_actual_variable_range(), which will include an index scan of the hypertable parent.In addition to being unneccessary, it can also cause problems in situations where the hypertable parent contains data as a result of a bug.
There is a check that an index scan is not done for a partitioned table, so we do the same here by setting the indexlist to NIL after hypertable expansion. The index list is needed while expanding the hypertables to construct correct index scans for chunks of a hypertable.