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Improvements for fast count() after #7510 #7551

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Oct 30, 2019
Merged

Improvements for fast count() after #7510 #7551

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6 changes: 6 additions & 0 deletions dbms/src/AggregateFunctions/AggregateFunctionCount.h
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Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,12 @@ class AggregateFunctionCount final : public IAggregateFunctionDataHelper<Aggrega
}

const char * getHeaderFilePath() const override { return __FILE__; }

/// Reset the state to specified value. This function is not the part of common interface.
void set(AggregateDataPtr place, UInt64 new_count)
{
data(place).count = new_count;
}
};


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6 changes: 1 addition & 5 deletions dbms/src/Interpreters/InterpreterSelectQuery.cpp
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Expand Up @@ -92,7 +92,6 @@
#include <Processors/Transforms/FinishSortingTransform.h>
#include <DataTypes/DataTypeAggregateFunction.h>
#include <DataStreams/materializeBlock.h>
#include <IO/MemoryReadWriteBuffer.h>


namespace DB
Expand Down Expand Up @@ -1313,10 +1312,7 @@ void InterpreterSelectQuery::executeFetchColumns(
agg_count.create(place);
SCOPE_EXIT(agg_count.destroy(place));

MemoryWriteBuffer out;
writeVarUInt(*num_rows, out);
auto in = out.tryGetReadBuffer();
agg_count.deserialize(place, *in, nullptr);
agg_count.set(place, *num_rows);

auto column = ColumnAggregateFunction::create(func);
column->insertFrom(place);
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