mirror of https://gitee.com/bigwinds/arangodb
101 lines
4.0 KiB
C++
101 lines
4.0 KiB
C++
////////////////////////////////////////////////////////////////////////////////
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/// DISCLAIMER
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///
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/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
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/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
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///
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/// Licensed under the Apache License, Version 2.0 (the "License");
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/// you may not use this file except in compliance with the License.
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/// You may obtain a copy of the License at
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///
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/// http://www.apache.org/licenses/LICENSE-2.0
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///
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/// Unless required by applicable law or agreed to in writing, software
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/// distributed under the License is distributed on an "AS IS" BASIS,
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/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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/// See the License for the specific language governing permissions and
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/// limitations under the License.
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///
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/// Copyright holder is ArangoDB GmbH, Cologne, Germany
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///
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/// @author Jan Steemann
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////////////////////////////////////////////////////////////////////////////////
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#ifndef ARANGOD_AQL_AGGREGATOR_H
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#define ARANGOD_AQL_AGGREGATOR_H 1
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#include "Aql/AqlValue.h"
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#include "Basics/Common.h"
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#include <velocypack/Slice.h>
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namespace arangodb {
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namespace transaction {
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class Methods;
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}
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namespace aql {
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struct Aggregator {
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Aggregator() = delete;
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Aggregator(Aggregator const&) = delete;
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Aggregator& operator=(Aggregator const&) = delete;
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explicit Aggregator(transaction::Methods* trx) : trx(trx) {}
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virtual ~Aggregator() = default;
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virtual void reset() = 0;
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virtual void reduce(AqlValue const&) = 0;
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virtual AqlValue stealValue() = 0;
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/// @brief creates an aggregator from a name string
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static std::unique_ptr<Aggregator> fromTypeString(transaction::Methods*,
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std::string const& type);
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/// @brief creates an aggregator from a velocypack slice
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static std::unique_ptr<Aggregator> fromVPack(transaction::Methods*,
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arangodb::velocypack::Slice const&,
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char const* nameAttribute);
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/// @brief return a pointer to an aggregator factory for an aggregator type
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/// throws if the aggregator cannot be found
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static std::function<std::unique_ptr<Aggregator>(transaction::Methods*)> const* factoryFromTypeString(
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std::string const& type);
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/// @brief translates an alias to an actual aggregator name
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/// returns the original value if the name was not an alias
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static std::string translateAlias(std::string const& name);
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/// @brief name/type of aggregator to use for the DB server part of the
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/// aggregation when a COLLECT is pushed from coordinator to DB server. for
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/// example, the MAX aggregator is commutative. it can be pushed from the
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/// coordinator to the DB server and be used as a MAX aggregator there too.
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/// other aggregators may need slight adjustment or type changes when they are
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/// pushed to DB servers an empty return value means that the aggregator is
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/// not suitable for being pushed to a DB server
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static std::string pushToDBServerAs(std::string const& type);
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/// @brief name/type of aggregator to use for the coordinator part of the
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/// aggregation when a COLLECT is pushed from coordinator to DB server. for
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/// example, the COUNT aggregator is commutative. it can be pushed from the
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/// coordinator to the DB server and be used there too. However, on the
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/// coordinator we must not use COUNT on the aggregated results from the DB
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/// server, but use SUM instead
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static std::string runOnCoordinatorAs(std::string const& type);
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/// @brief whether or not the aggregator name is supported and part of the
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/// public API. all internal-only aggregators count as not supported here
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static bool isValid(std::string const& type);
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/// @brief whether or not the aggregator requires any input or if the input
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/// can be optimized away (note current: COUNT/LENGTH don't, all others do)
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static bool requiresInput(std::string const& type);
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protected:
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transaction::Methods* trx;
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};
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} // namespace aql
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} // namespace arangodb
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#endif
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