release-19.2: opt: don't zigzag redundantly #42186
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Previously, we would zigzag on any pair of indexes where both had a prefix constrained by the fixed cols. This restriction can be strengthened: it's pointless to zigzag on any pair of indexes where the fixed cols of one are a subset of the fixed cols of another. Adding this restriction prevents cases like zigzagging on two identical indexes (which can come up in certain stats scenarios that I do not fully understand yet). Release note (sql change): Restricted the set of zigzag joins that are planned to those which have a chance at being beneficial.
RaduBerinde
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LGTM, thanks for backporting! |
spaskob
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release-19.2: opt: don't zigzag redundantly
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Backport 1/1 commits from #42159.
/cc @cockroachdb/release
Previously, we would zigzag on any pair of indexes where both had a
prefix constrained by the fixed cols. This restriction can be
strengthened: it's pointless to zigzag on any pair of indexes where the
fixed cols of one are a subset of the fixed cols of another. Adding this
restriction prevents cases like zigzagging on two identical indexes
(which can come up in certain stats scenarios that I do not fully
understand yet).
Release note (sql change): Restricted the set of zigzag joins that are
planned to those which have a chance at being beneficial.