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MCOL-5153 This patch replaces MDB collation aware hash function with the (#2488)

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exact functionality that does not use MDB hash function.
This patch also takes a bit from Robin Hood hash map implementation forgotten
that reduces hash function collision rate.
This commit is contained in:
Roman Nozdrin
2022-08-07 02:36:03 +03:00
committed by GitHub
parent af9caf8d6e
commit dd96e686c0
4 changed files with 59 additions and 15 deletions
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14
utils/rowgroup/rowstorage.h
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@ -36,6 +36,9 @@ class RowGroupStorage;
uint64_t hashRow(const rowgroup::Row& r, std::size_t lastCol);
constexpr const size_t MaxConstStrSize = 2048ULL;
constexpr const size_t MaxConstStrBufSize = MaxConstStrSize << 1;
class RowAggStorage
{
public:
@ -161,6 +164,9 @@ class RowAggStorage
*/
inline void rowHashToIdx(uint64_t h, uint32_t& info, size_t& idx, const Data* curData) const
{
// An addition from the original robin hood HM.
h *= fCurData->hashMultiplier_;
h ^= h >> 33U;
info = curData->fInfoInc + static_cast<uint32_t>((h & INFO_MASK) >> curData->fInfoHashShift);
idx = (h >> INIT_INFO_BITS) & curData->fMask;
}
@ -230,6 +236,13 @@ class RowAggStorage
info = fCurData->fInfo[idx];
}
void nextHashMultiplier()
{
// adding an *even* number, so that the multiplier will always stay odd. This is necessary
// so that the hash stays a mixing function (and thus doesn't have any information loss).
fCurData->hashMultiplier_ += 0xc4ceb9fe1a85ec54;
}
/** @brief Increase internal data size if needed
*/
void increaseSize();
@ -325,6 +338,7 @@ class RowAggStorage
size_t fSize{0};
size_t fMask{0};
size_t fMaxSize{0};
uint64_t hashMultiplier_{0xc4ceb9fe1a85ec53ULL};
uint32_t fInfoInc{INIT_INFO_INC};
uint32_t fInfoHashShift{INIT_INFO_HASH_SHIFT};
};