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#pragma once
#include <Common/HashTable/StringHashTable.h>
template <typename SubMaps, typename ImplTable = StringHashTable<SubMaps>, size_t BITS_FOR_BUCKET = 8>
class TwoLevelStringHashTable : private boost::noncopyable
{
protected:
using HashValue = size_t;
using Self = TwoLevelStringHashTable;
public:
using Key = StringRef;
using Impl = ImplTable;
static constexpr UInt32 NUM_BUCKETS = 1ULL << BITS_FOR_BUCKET;
static constexpr UInt32 MAX_BUCKET = NUM_BUCKETS - 1;
// TODO: currently hashing contains redundant computations when doing distributed or external aggregations
size_t hash(const Key & x) const
{
return const_cast<Self &>(*this).dispatch(*this, x, [&](const auto &, const auto &, size_t hash) { return hash; });
}
size_t operator()(const Key & x) const { return hash(x); }
/// NOTE Bad for hash tables with more than 2^32 cells.
static size_t getBucketFromHash(size_t hash_value) { return (hash_value >> (32 - BITS_FOR_BUCKET)) & MAX_BUCKET; }
using key_type = typename Impl::key_type;
using mapped_type = typename Impl::mapped_type;
using value_type = typename Impl::value_type;
using cell_type = typename Impl::cell_type;
using LookupResult = typename Impl::LookupResult;
using ConstLookupResult = typename Impl::ConstLookupResult;
Impl impls[NUM_BUCKETS];
TwoLevelStringHashTable() = default;
template <typename Source>
explicit TwoLevelStringHashTable(const Source & src)
{
if (src.m0.hasZero())
impls[0].m0.setHasZero(*src.m0.zeroValue());
for (auto & v : src.m1)
{
size_t hash_value = v.getHash(src.m1);
size_t buck = getBucketFromHash(hash_value);
impls[buck].m1.insertUniqueNonZero(&v, hash_value);
}
for (auto & v : src.m2)
{
size_t hash_value = v.getHash(src.m2);
size_t buck = getBucketFromHash(hash_value);
impls[buck].m2.insertUniqueNonZero(&v, hash_value);
}
for (auto & v : src.m3)
{
size_t hash_value = v.getHash(src.m3);
size_t buck = getBucketFromHash(hash_value);
impls[buck].m3.insertUniqueNonZero(&v, hash_value);
}
for (auto & v : src.ms)
{
size_t hash_value = v.getHash(src.ms);
size_t buck = getBucketFromHash(hash_value);
impls[buck].ms.insertUniqueNonZero(&v, hash_value);
}
}
// This function is mostly the same as StringHashTable::dispatch, but with
// added bucket computation. See the comments there.
template <typename Self, typename Func, typename KeyHolder>
static auto ALWAYS_INLINE dispatch(Self & self, KeyHolder && key_holder, Func && func)
{
StringHashTableHash hash;
const StringRef & x = keyHolderGetKey(key_holder);
const size_t sz = x.size;
if (sz == 0)
{
keyHolderDiscardKey(key_holder);
return func(self.impls[0].m0, VoidKey{}, 0);
}
if (x.data[x.size - 1] == 0)
{
// Strings with trailing zeros are not representable as fixed-size
// string keys. Put them to the generic table.
auto res = hash(x);
auto buck = getBucketFromHash(res);
return func(self.impls[buck].ms, std::forward<KeyHolder>(key_holder),
res);
}
const char * p = x.data;
// pending bits that needs to be shifted out
const char s = (-sz & 7) * 8;
union
{
StringKey8 k8;
StringKey16 k16;
StringKey24 k24;
UInt64 n[3];
};
switch ((sz - 1) >> 3)
{
case 0:
{
// first half page
if ((reinterpret_cast<uintptr_t>(p) & 2048) == 0)
{
memcpy(&n[0], p, 8);
if constexpr (std::endian::native == std::endian::little)
n[0] &= -1ULL >> s;
else
n[0] &= -1ULL << s;
}
else
{
const char * lp = x.data + x.size - 8;
memcpy(&n[0], lp, 8);
if constexpr (std::endian::native == std::endian::little)
n[0] >>= s;
else
n[0] <<= s;
}
auto res = hash(k8);
auto buck = getBucketFromHash(res);
keyHolderDiscardKey(key_holder);
return func(self.impls[buck].m1, k8, res);
}
case 1:
{
memcpy(&n[0], p, 8);
const char * lp = x.data + x.size - 8;
memcpy(&n[1], lp, 8);
if constexpr (std::endian::native == std::endian::little)
n[1] >>= s;
else
n[1] <<= s;
auto res = hash(k16);
auto buck = getBucketFromHash(res);
keyHolderDiscardKey(key_holder);
return func(self.impls[buck].m2, k16, res);
}
case 2:
{
memcpy(&n[0], p, 16);
const char * lp = x.data + x.size - 8;
memcpy(&n[2], lp, 8);
if constexpr (std::endian::native == std::endian::little)
n[2] >>= s;
else
n[2] <<= s;
auto res = hash(k24);
auto buck = getBucketFromHash(res);
keyHolderDiscardKey(key_holder);
return func(self.impls[buck].m3, k24, res);
}
default:
{
auto res = hash(x);
auto buck = getBucketFromHash(res);
return func(self.impls[buck].ms, std::forward<KeyHolder>(key_holder), res);
}
}
}
template <typename KeyHolder>
void ALWAYS_INLINE emplace(KeyHolder && key_holder, LookupResult & it, bool & inserted)
{
dispatch(*this, key_holder, typename Impl::EmplaceCallable{it, inserted});
}
LookupResult ALWAYS_INLINE find(const Key x)
{
return dispatch(*this, x, typename Impl::FindCallable{});
}
ConstLookupResult ALWAYS_INLINE find(const Key x) const
{
return dispatch(*this, x, typename Impl::FindCallable{});
}
void write(DB::WriteBuffer & wb) const
{
for (UInt32 i = 0; i < NUM_BUCKETS; ++i)
impls[i].write(wb);
}
void writeText(DB::WriteBuffer & wb) const
{
for (UInt32 i = 0; i < NUM_BUCKETS; ++i)
{
if (i != 0)
DB::writeChar(',', wb);
impls[i].writeText(wb);
}
}
void read(DB::ReadBuffer & rb)
{
for (UInt32 i = 0; i < NUM_BUCKETS; ++i)
impls[i].read(rb);
}
void readText(DB::ReadBuffer & rb)
{
for (UInt32 i = 0; i < NUM_BUCKETS; ++i)
{
if (i != 0)
DB::assertChar(',', rb);
impls[i].readText(rb);
}
}
size_t size() const
{
size_t res = 0;
for (UInt32 i = 0; i < NUM_BUCKETS; ++i)
res += impls[i].size();
return res;
}
bool empty() const
{
for (UInt32 i = 0; i < NUM_BUCKETS; ++i)
if (!impls[i].empty())
return false;
return true;
}
size_t getBufferSizeInBytes() const
{
size_t res = 0;
for (UInt32 i = 0; i < NUM_BUCKETS; ++i)
res += impls[i].getBufferSizeInBytes();
return res;
}
};
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