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5f1e65b252
This implements a new function for approximate computation of the most frequent entries using Filtered Space Saving with a merge step adapted from Parallel Space Saving paper. It works better for cases where GROUP BY x is impractical due to high cardinality of x, such as top IP addresses or top search queries.
71 lines
2.5 KiB
C++
71 lines
2.5 KiB
C++
#include <AggregateFunctions/AggregateFunctionFactory.h>
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#include <AggregateFunctions/AggregateFunctionTopK.h>
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#include <AggregateFunctions/Helpers.h>
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namespace DB
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{
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namespace
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{
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/// Substitute return type for Date and DateTime
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class AggregateFunctionTopKDate : public AggregateFunctionTopK<DataTypeDate::FieldType>
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{
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DataTypePtr getReturnType() const override { return std::make_shared<DataTypeArray>(std::make_shared<DataTypeDate>()); }
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};
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class AggregateFunctionTopKDateTime : public AggregateFunctionTopK<DataTypeDateTime::FieldType>
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{
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DataTypePtr getReturnType() const override { return std::make_shared<DataTypeArray>(std::make_shared<DataTypeDateTime>()); }
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};
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static IAggregateFunction * createWithExtraTypes(const IDataType & argument_type)
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{
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if (typeid_cast<const DataTypeDate *>(&argument_type)) return new AggregateFunctionTopKDate;
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else if (typeid_cast<const DataTypeDateTime *>(&argument_type)) return new AggregateFunctionTopKDateTime;
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else
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{
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/// Check that we can use plain version of AggregateFunctionTopKGeneric
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if (typeid_cast<const DataTypeString*>(&argument_type) || typeid_cast<const DataTypeFixedString*>(&argument_type))
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return new AggregateFunctionTopKGeneric<true>;
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auto * array_type = typeid_cast<const DataTypeArray *>(&argument_type);
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if (array_type)
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{
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auto nested_type = array_type->getNestedType();
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if (nested_type->isNumeric() || typeid_cast<DataTypeFixedString *>(nested_type.get()))
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return new AggregateFunctionTopKGeneric<true>;
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}
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return new AggregateFunctionTopKGeneric<false>;
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}
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}
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AggregateFunctionPtr createAggregateFunctionTopK(const std::string & name, const DataTypes & argument_types)
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{
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if (argument_types.size() != 1)
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throw Exception("Incorrect number of arguments for aggregate function " + name,
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ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
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AggregateFunctionPtr res(createWithNumericType<AggregateFunctionTopK>(*argument_types[0]));
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if (!res)
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res = AggregateFunctionPtr(createWithExtraTypes(*argument_types[0]));
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if (!res)
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throw Exception("Illegal type " + argument_types[0]->getName() +
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" of argument for aggregate function " + name, ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
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return res;
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}
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}
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void registerAggregateFunctionTopK(AggregateFunctionFactory & factory)
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{
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factory.registerFunction("topK", createAggregateFunctionTopK);
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}
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}
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