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Reduce maximum allowable size of |HashSet|.

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This commit is contained in:
Ivan Lezhankin 2018-10-25 16:17:29 +03:00
parent 68138a76f8
commit 0592081f2f
1 changed files with 6 additions and 2 deletions
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8
dbms/src/AggregateFunctions/AggregateFunctionUniqCombined.h
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@ -71,7 +71,11 @@ struct AggregateFunctionUniqCombinedDataWithKey
{
// TODO(ilezhankin): pre-generate values for |UniqCombinedBiasData|,
// at the moment gen-bias-data.py script doesn't work.
using Set = CombinedCardinalityEstimator<Key, HashSet<Key, TrivialHash, HashTableGrower<>>, 16, K - 3, K, TrivialHash, Key>;
// We want to migrate from |HashSet| to |HyperLogLogCounter| when the sizes in memory become almost equal.
// The size per element in |HashSet| is sizeof(Key)*2 bytes, and the overall size of |HyperLogLogCounter| is 2^K * 6 bits.
// For Key=UInt32 we can calculate: 2^X * 4 * 2 ≤ 2^(K-3) * 6 ⇒ X ≤ K-4.
using Set = CombinedCardinalityEstimator<Key, HashSet<Key, TrivialHash, HashTableGrower<>>, 16, K - 4, K, TrivialHash, Key>;
Set set;
};
@ -82,7 +86,7 @@ struct AggregateFunctionUniqCombinedDataWithKey<Key, 17>
using Set = CombinedCardinalityEstimator<Key,
HashSet<Key, TrivialHash, HashTableGrower<>>,
16,
14,
13,
17,
TrivialHash,
Key,