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release-23.2: opt: fix inverted index constrained scans for equality filters #112791

Merged
merged 2 commits into from
Oct 20, 2023
Merged

release-23.2: opt: fix inverted index constrained scans for equality filters #112791

merged 2 commits into from
Oct 20, 2023

Commits on Oct 18, 2023

  1. opt: fix inverted index constrained scans for equality filters 

    This commit fixes a bug introduced in #101178 that allows the optimizer
to generated inverted index scans on columns that are not filtered by
the query. For example, an inverted index over the column `j1` could be
scanned for a filter involving a different column, like `j2 = '5'`. The
bug is caused by a simple omission of code that must check that the
column in the filter is an indexed column.

Fixes #111963

There is no release note because this bug is not present in any
releases.

Release note: None
    @mgartner
    mgartner committed Oct 18, 2023
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  2. randgen: generate single-column indexes more often 

    This commit makes `randgen` more likely to generate single-column
indexes. It is motivated by the bug #111963, which surprisingly lived on
the master branch for sixth months without being detected. It's not
entirely clear why TLP or other randomized tests did not catch the bug,
which has such a simple reproduction.

One theory is that indexes tend to be multi-column and constrained scans
on multi-column inverted indexes are not commonly planned for randomly
generated queries because the set of requirements to generate the scan
are very specific: the query must hold each prefix column constant, e.g.
`a=1 AND b=2 AND j='5'::JSON`. The likelihood of randomly generating
such an expression may be so low that the bug was not caught.

By making 50% of indexes single-column, this bug may have been more
likely to be caught because only the inverted index column needs to be
constrained by an equality filter.

Release note: None
    @mgartner
    mgartner committed Oct 18, 2023
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