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/**
* Copyright (C) 2024-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/bson/bsonobj.h"
#include "mongo/db/cursor_id.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/query/plan_yield_policy.h"
#include "mongo/executor/task_executor_cursor_parameters_gen.h"
namespace mongo {
namespace executor {
/**
* TaskExecutorCursorGetMoreStrategy is an abstract class that allows for customization of the logic
* a TaskExecutorCursor uses to configure GetMore requests and toggle pre-fetching of those
* GetMores.
*/
class TaskExecutorCursorGetMoreStrategy {
public:
/**
* Generates a BSONObj that represents the next getMore command to be dispatched. Some
* implementations (e.g., MongotTaskExecutorCursorGetMoreStrategy) may change internal state
* (like batchSize) per batch, with the assumption that each call is for the subsequent batch.
* For that reason, it's important this method is only called once per batch.
*
* The CursorId and NamespaceString are necessary to be included in the command obj, and
* prevBatchNumReceived may be used to configure the request options (again, like batchSize).
*/
virtual BSONObj createGetMoreRequest(const CursorId& cursorId,
const NamespaceString& nss,
long long prevBatchNumReceived,
long long totalNumReceived) = 0;
/**
* If true, we'll fetch the next batch as soon as the current one is received. If false, we'll
* fetch the next batch when the current batch is exhausted and 'getNext()' is invoked.
*
* totalNumReceived and numBatchesReceived may or may not be used, based on implementation, to
* determine if prefetch is enabled.
*/
virtual bool shouldPrefetch(long long totalNumReceived, long long numBatchesReceived) const = 0;
virtual ~TaskExecutorCursorGetMoreStrategy() {}
};
/**
* The default implementation of TaskExecutorCursorGetMoreStrategy simply holds a batchSize and
* preFetchNextBatch flag that are used for all successive GetMore requests.
*/
class DefaultTaskExecutorCursorGetMoreStrategy final : public TaskExecutorCursorGetMoreStrategy {
public:
DefaultTaskExecutorCursorGetMoreStrategy(boost::optional<int64_t> batchSize = boost::none,
bool preFetchNextBatch = true)
: _batchSize(batchSize), _preFetchNextBatch(preFetchNextBatch) {}
DefaultTaskExecutorCursorGetMoreStrategy(DefaultTaskExecutorCursorGetMoreStrategy&& other) =
default;
~DefaultTaskExecutorCursorGetMoreStrategy() final {}
BSONObj createGetMoreRequest(const CursorId& cursorId,
const NamespaceString& nss,
long long prevBatchNumReceived,
long long totalNumReceived) final;
bool shouldPrefetch(long long totalNumReceived, long long numBatchesReceived) const final {
return _preFetchNextBatch;
}
private:
const boost::optional<int64_t> _batchSize;
const bool _preFetchNextBatch;
};
struct TaskExecutorCursorOptions {
/**
* Construct the options from any pre-constructed GetMore strategy.
*/
TaskExecutorCursorOptions(std::shared_ptr<TaskExecutorCursorGetMoreStrategy> getMoreStrategy =
std::make_shared<DefaultTaskExecutorCursorGetMoreStrategy>(),
std::shared_ptr<PlanYieldPolicy> yieldPolicy = nullptr,
bool pinConnection = gPinTaskExecCursorConns.load());
/**
* Construct the options with the default GetMore strategy from a given batchSize and
* preFetchNextBatch flag.
*/
TaskExecutorCursorOptions(boost::optional<int64_t> batchSize,
bool preFetchNextBatch = true,
std::shared_ptr<PlanYieldPolicy> yieldPolicy = nullptr,
bool pinConnection = gPinTaskExecCursorConns.load());
TaskExecutorCursorOptions(TaskExecutorCursorOptions& other) = default;
TaskExecutorCursorOptions(TaskExecutorCursorOptions&& other) = default;
// Specifies the strategy with which the cursor should configure GetMore requests.
// Using shared_ptr to allow tries on network failure, don't share the pointer on other
// purpose.
std::shared_ptr<TaskExecutorCursorGetMoreStrategy> getMoreStrategy;
// Optional yield policy allows us to yield(release storage resources) during remote call.
// Using shared_ptr to allow tries on network failure, don't share the pointer on other
// purpose. In practice, this will always be of type PlanYieldPolicyRemoteCursor, but
// for dependency reasons, we must use the generic PlanYieldPolicy here.
std::shared_ptr<PlanYieldPolicy> yieldPolicy;
bool pinConnection;
};
} // namespace executor
} // namespace mongo
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