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docs/reference/aggregations/metrics
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lines changed Original file line number Diff line number Diff line change @@ -150,10 +150,18 @@ public static void main(String[] args) {
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image:images/cardinality_error.png[]
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- For all 3 thresholds, counts have been accurate up to the configured threshold
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- (although not guaranteed, this is likely to be the case). Please also note that
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- even with a threshold as low as 100, the error remains very low, even when
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- counting millions of items.
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+ For all 3 thresholds, counts have been accurate up to the configured threshold.
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+ Although not guaranteed, this is likely to be the case. Accuracy in practice depends
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+ on the dataset in question. In general, most datasets show consistently good
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+ accuracy. Also note that even with a threshold as low as 100, the error
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+ remains very low (1-6% as seen in the above graph) even when counting millions of items.
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+
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+ The HyperLogLog++ algorithm depends on the leading zeros of hashed
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+ values, the exact distributions of hashes in a dataset can affect the
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+ accuracy of the cardinality.
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+
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+ Please also note that even with a threshold as low as 100, the error remains
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+ very low, even when counting millions of items.
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==== Pre-computed hashes
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