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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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41
utils/rowgroup/rowstorage.cpp
View File

@ -166,10 +166,24 @@ uint64_t hashRow(const rowgroup::Row& r, std::size_t lastCol)
case execplan::CalpontSystemCatalog::VARCHAR:
case execplan::CalpontSystemCatalog::BLOB:
case execplan::CalpontSystemCatalog::TEXT:
h.add(r.getCharset(i), r.getConstString(i));
strHashUsed = true;
{
auto strColValue = r.getConstString(i);
if (strColValue.length() > MaxConstStrSize)
{
h.add(r.getCharset(i), strColValue);
strHashUsed = true;
}
else
{
auto cs = r.getCharset(i);
uchar buf[MaxConstStrBufSize];
uint nActualWeights = cs->strnxfrm(buf, MaxConstStrBufSize, MaxConstStrBufSize,
reinterpret_cast<const uchar*>(strColValue.str()), strColValue.length(),
datatypes::Charset::getDefaultFlags());
ret = hashData(buf, nActualWeights, ret);
}
break;
}
default: ret = hashData(r.getData() + r.getOffset(i), r.getColumnWidth(i), ret); break;
}
}
@ -1820,15 +1834,26 @@ void RowAggStorage::increaseSize()
if (fCurData->fSize * maxMaskMultiplierWoRehashing < calcMaxSize(fCurData->fMask + 1))
{
// something strange happens...
throw logging::IDBExcept(logging::IDBErrorInfo::instance()->errorMsg(logging::ERR_DISKAGG_ERROR),
logging::ERR_DISKAGG_ERROR);
throw logging::IDBExcept(logging::IDBErrorInfo::instance()->errorMsg(logging::ERR_DISKAGG_OVERFLOW2),
logging::ERR_DISKAGG_OVERFLOW2);
}
auto freeMem = fMM->getFree();
if (fEnabledDiskAggregation ||
freeMem > (fMM->getUsed() + fCurData->fHashes->memUsage() + fStorage->getAproxRGSize()) * 2)
{
rehashPowerOfTwo((fCurData->fMask + 1) * 2);
if (fCurData->fSize * 2 < maxSize)
{
// we have to resize, even though there would still be plenty of space left!
// Try to rehash instead. Delete freed memory so we don't steadyily increase mem in case
// we have to rehash a few times
nextHashMultiplier();
rehashPowerOfTwo(fCurData->fMask + 1);
}
else
{
rehashPowerOfTwo((fCurData->fMask + 1) * 2);
}
}
else if (fGeneration < MAX_INMEMORY_GENS - 1)
{
@ -1888,8 +1913,8 @@ void RowAggStorage::insertSwap(size_t oldIdx, RowPosHashStorage* oldHashes)
{
if (fCurData->fMaxSize == 0 && !tryIncreaseInfo())
{
throw logging::IDBExcept(logging::IDBErrorInfo::instance()->errorMsg(logging::ERR_DISKAGG_ERROR),
logging::ERR_DISKAGG_ERROR);
throw logging::IDBExcept(logging::IDBErrorInfo::instance()->errorMsg(logging::ERR_DISKAGG_OVERFLOW1),
logging::ERR_DISKAGG_OVERFLOW1);
}
size_t idx{};

14
utils/rowgroup/rowstorage.h
View File

@ -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};
};