feat: support HLL sketch functions - #24611
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XuPeng-SH
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Reviewed from multiple angles. The HLL agg/scalar wiring is complete, NULL/invalid-sketch semantics are covered, and I did not find a blocking correctness issue.
aunjgr
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heni02
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What type of PR is this?
Which issue(s) this PR fixes:
issue #23356
What this PR does / why we need it:
This PR adds HyperLogLog sketch functions for approximate distinct counting:
hll_add_agg(expr)builds a serialized HLL sketch from non-NULL input values.hll_merge_agg(sketch)merges serialized HLL sketches frombinary/varbinary/blobinputs.hll_cardinality(sketch)returns the estimated cardinality of a serialized HLL sketch.The current implementation stores HLL sketches as
varbinary/blobvalues and does not add a dedicated SQLHLLtype yet.Validation:
git diff --checkCGO_CFLAGS="-I$(pwd)/thirdparties/install/include" go test ./pkg/sql/colexec/aggexec -count=1CGO_CFLAGS="-I$(pwd)/thirdparties/install/include" go test ./pkg/sql/plan/function -count=1CGO_CFLAGS="-I$(pwd)/thirdparties/install/include" go test ./pkg/sql/plan -run '^$' -count=1CGO_CFLAGS="-I$(pwd)/thirdparties/install/include" go test ./pkg/sql/colexec/aggexec ./pkg/sql/plan/function -run 'TestHll|TestApproxCount|Test_funids' -count=1mo-servicelocally and rantest/distributed/cases/function/func_hll.sqlagainst a temporary MatrixOne service on port16001; valid HLL queries returned3,2,2,3,0,NULL, and invalid sketch input returnedinvalid input: invalid HLL sketch: too short binary.