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Faster path for varint read.

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clickhouse-benchmark <<< 'select count() from s where not ignore(s);'

before this patch:

```

QPS: 0.732, RPS: 2346562049.608, MiB/s: 22378.560, result RPS: 0.732, result MiB/s: 0.000.
0.000%  1.310 sec.
10.000% 1.321 sec.
20.000% 1.327 sec.
30.000% 1.337 sec.
40.000% 1.343 sec.
50.000% 1.359 sec.
60.000% 1.366 sec.
70.000% 1.381 sec.
80.000% 1.400 sec.
90.000% 1.434 sec.
95.000% 1.448 sec.
99.000% 1.489 sec.
99.900% 1.499 sec.
99.990% 1.500 sec.

```

after this patch:

```
QPS: 0.787, RPS: 2524560389.064, MiB/s: 24076.084, result RPS: 0.787, result MiB/s: 0.000.
0.000%  1.228 sec.
10.000% 1.232 sec.
20.000% 1.235 sec.
30.000% 1.241 sec.
40.000% 1.246 sec.
50.000% 1.256 sec.
60.000% 1.265 sec.
70.000% 1.278 sec.
80.000% 1.296 sec.
90.000% 1.321 sec.
95.000% 1.354 sec.
99.000% 1.421 sec.
99.900% 1.453 sec.
99.990% 1.456 sec.
```

I also tried a SSE2 implementation and it's much slower (50%)
This commit is contained in:
Amos Bird 2018-08-26 02:23:26 +08:00
parent 0ef5b19436
commit a589230249
1 changed files with 12 additions and 3 deletions
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15
dbms/src/IO/VarInt.h
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@ -118,13 +118,15 @@ inline void throwReadAfterEOF()
throw Exception("Attempt to read after eof", ErrorCodes::ATTEMPT_TO_READ_AFTER_EOF);
}
inline void readVarUInt(UInt64 & x, ReadBuffer & istr)
template<bool fast>
inline void readVarUIntImpl(UInt64 & x, ReadBuffer & istr)
{
x = 0;
for (size_t i = 0; i < 9; ++i)
{
if (istr.eof())
throwReadAfterEOF();
if constexpr (!fast)
if (istr.eof())
throwReadAfterEOF();
UInt64 byte = *istr.position();
++istr.position();
@ -135,6 +137,13 @@ inline void readVarUInt(UInt64 & x, ReadBuffer & istr)
}
}
inline void readVarUInt(UInt64 & x, ReadBuffer & istr)
{
if (istr.buffer().end() - istr.position() >= 9)
return readVarUIntImpl<true>(x, istr);
return readVarUIntImpl<false>(x, istr);
}
inline void readVarUInt(UInt64 & x, std::istream & istr)
{