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fix(rowstorage): SplitMix64 PRNG implementation to replace stdlib MT … #3050

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Merged
merged 1 commit into from
Dec 5, 2023
+19 −8
Merged

fix(rowstorage): SplitMix64 PRNG implementation to replace stdlib MT … #3050

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8 changes: 3 additions & 5 deletions utils/rowgroup/rowstorage.cpp
View file
Original file line number Diff line number Diff line change
@@ -1495,9 +1495,7 @@ RowAggStorage::RowAggStorage(const std::string& tmpDir, RowGroup* rowGroupOut, R
, fTmpDir(tmpDir)
, fRowGroupOut(rowGroupOut)
, fKeysRowGroup(keysRowGroup)
, fRD()
, fRandGen(fRD())
, fRandDistr(0, 100)
, fRandom(reinterpret_cast<std::uintptr_t>(this))
{
char suffix[PATH_MAX];
snprintf(suffix, sizeof(suffix), "/p%u-t%p/", getpid(), this);
@@ -1683,15 +1681,15 @@ void RowAggStorage::dump()
break;
}

int64_t totalMem = fMM->getConfigured();
const int64_t totalMem = fMM->getConfigured();
// If the generations are allowed and there are less than half of
// rowgroups in memory, then we start a new generation
if (fAllowGenerations && fStorage->fLRU->size() < fStorage->fRGDatas.size() / 2 &&
fStorage->fRGDatas.size() > 10)
{
startNewGeneration();
}
else if (fAllowGenerations && freeMem < totalMem / 10 * 3 && fRandDistr(fRandGen) < 30)
else if (fAllowGenerations && freeMem < totalMem / 10 * 3 && nextRandDistib() < 30)
{
startNewGeneration();
}
19 changes: 16 additions & 3 deletions utils/rowgroup/rowstorage.h
View file
Original file line number Diff line number Diff line change
@@ -311,6 +311,21 @@ class RowAggStorage
static constexpr uint8_t INIT_INFO_HASH_SHIFT{0};
static constexpr uint16_t MAX_INMEMORY_GENS{4};

// This is SplitMix64 implementation borrowed from here
// https://thompsonsed.co.uk/random-number-generators-for-c-performance-tested
inline uint64_t nextRandom()
{
uint64_t z = (fRandom += UINT64_C(0x9E3779B97F4A7C15));
z = (z ^ (z >> 30)) * UINT64_C(0xBF58476D1CE4E5B9);
z = (z ^ (z >> 27)) * UINT64_C(0x94D049BB133111EB);
return z ^ (z >> 31);
}

inline uint64_t nextRandDistib()
{
return nextRandom() % 100;
}

struct Data
{
RowPosHashStoragePtr fHashes;
@@ -349,9 +364,7 @@ class RowAggStorage
bool fInitialized{false};
rowgroup::RowGroup* fRowGroupOut;
rowgroup::RowGroup* fKeysRowGroup;
std::random_device fRD;
std::mt19937 fRandGen;
std::uniform_int_distribution<uint8_t> fRandDistr;
uint64_t fRandom = 0xc4ceb9fe1a85ec53ULL; // initial integer to set PRNG up
};

} // namespace rowgroup