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dbms: aggregate function quantileTiming: added (deterministic) randomization [#CONV-2944].

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This commit is contained in:
Alexey Milovidov 2013-10-20 03:57:28 +00:00
parent 6c1b8aadd0
commit 9a4d300a10
1 changed files with 11 additions and 2 deletions
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13
dbms/include/DB/AggregateFunctions/AggregateFunctionQuantileTiming.h
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@ -12,6 +12,8 @@
#include <DB/Columns/ColumnArray.h>
#include <stats/IntHash.h>
namespace DB
{
@ -136,6 +138,13 @@ namespace detail
/// Число значений для каждого значения от small_threshold до big_threshold, округлённого до big_precision.
UInt64 count_big[BIG_SIZE];
/// Получить значение квантиля по индексу в массиве count_big.
static inline UInt16 indexInBigToValue(size_t i)
{
return (i * BIG_PRECISION) + SMALL_THRESHOLD
+ (intHash32<0>(i) % BIG_PRECISION - (BIG_PRECISION / 2)); /// Небольшая рандомизация, чтобы не было заметно, что все значения чётные.
}
public:
QuantileTimingLarge()
{
@ -209,7 +218,7 @@ namespace detail
}
if (i < BIG_SIZE)
return (i * BIG_PRECISION) + SMALL_THRESHOLD;
return indexInBigToValue(i);
return BIG_THRESHOLD;
}
@ -258,7 +267,7 @@ namespace detail
if (i < BIG_SIZE)
{
*result = (i * BIG_PRECISION) + SMALL_THRESHOLD;
*result = indexInBigToValue(i);
++level;
++result;