[7.17] Avoid doing I/O when fetching min and max for keyword fields (#92026) #92865
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javanna
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…#92026) Whenever sorting on a date, numeric or keyword field (as primary sort), the can_match phase retrieves min and max for the field and sorts the shards (asc or desc depending on the sort order) so that they are going to be queried following that order. This allows incremental results to be exposed in that same order when using async search, as well as optimizations built on top of such behaviour (elastic#51852). For fields with points we call `getMinPackedValue` and `getMaxPackedValue`, while for keyword fields we call `Terms#getMin` and `Terms#getMax`. Elasticsearch uses `FilterTerms` implementations to cancel queries as well as to track field usage. Such filter implementations should delegate their `getMin` and `getMax` calls to the wrapped `Terms` instance, which will leverage info from the block tree that caches min and max, otherwise they are always going to be retrieved from the index, which does I/O and slows the can_match phase down.
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Whenever sorting on a date, numeric or keyword field (as primary sort), the can_match phase retrieves min and max for the field and sorts the shards (asc or desc depending on the sort order) so that they are going to be queried following that order. This allows incremental results to be exposed in that same order when using async search, as well as optimizations built on top of such behaviour (#51852).
For fields with points we call
getMinPackedValueandgetMaxPackedValue, while for keyword fields we callTerms#getMinandTerms#getMax. Elasticsearch usesFilterTermsimplementations to cancel queries as well as to track field usage. Such filter implementations should delegate theirgetMinandgetMaxcalls to the wrappedTermsinstance, which will leverage info from the block tree that caches min and max, otherwise they are always going to be retrieved from the index, which does I/O and slows the can_match phase down.