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Type:
Improvement
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Resolution: Unresolved
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Priority:
Minor - P4
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None
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Affects Version/s: None
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Component/s: None
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Query Execution
We currently support bounding clustered collection scans when there's a comparison match expression on the cluster key: https://github.com/10gen/mongo/blob/fd275f66b712e0af181b53575efbe8a87f214a5e/src/mongo/db/query/planner_access.cpp#L267-L272
It should be easy to support the $regex operator when the query and collection collators match using the existing IndexBoundsBuilder. Something like this:
IndexEntry ie{BSON("_id"_sd << 1),
IndexType::INDEX_BTREE,
IndexDescriptor::IndexVersion::kV2,
false,
{},
{},
false,
true,
CoreIndexInfo::Identifier("clustered"),
nullptr,
{},
params.clusteredCollectionCollator,
nullptr};
OrderedIntervalList oil;
IndexBoundsBuilder::BoundsTightness bt;
IndexBoundsBuilder::translateRegex(regexExpr, BSON("_id"_sd << 1).firstElement(), ie, &oil, &bt);
const auto& interval = oil.intervals.front(); // second interval is for regex objects, not possible in _id
setMinRecord(collScan, record_id_helpers::keyForElem(interval.start, nullptr));
setMaxRecord(collScan, record_id_helpers::keyForElem(interval.end, nullptr));