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/**
* Copyright (C) 2018-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/db/exec/plan_stage.h"
#include "mongo/db/s/scoped_collection_metadata.h"
namespace mongo {
/**
* This stage drops documents that didn't belong to the shard we're executing on at the time of
* construction. This matches the contract for sharded cursorids which guarantees that a
* StaleConfigException will be thrown early or the cursorid for its entire lifetime will return
* documents matching the shard version set on the connection at the time of cursorid creation.
*
* A related system will ensure that the data migrated away from a shard will not be deleted as
* long as there are active queries from before the migration. Currently, "active queries" is
* defined by cursorids so it is important that the metadata used in this stage uses the same
* version as the cursorid. Therefore, you must wrap any Runner using this Stage in a
* ClientCursor during the same lock grab as constructing the Runner.
*
* BEGIN NOTE FROM GREG
*
* There are three sharded query contracts:
*
* 0) Migration commit takes the db lock - i.e. is serialized with writes and reads.
* 1) No data should be returned from a query in ranges of migrations that committed after the
* query started, or from ranges not owned when the query began.
* 2) No migrated data should be removed from a shard while there are queries that were active
* before the migration.
*
* As implementation details, collection metadata is used to determine the ranges of all data
* not actively migrated (or orphaned). CursorIds are currently used to establish "active"
* queries before migration commit.
*
* Combining all this: if a query is started in a db lock and acquires in that (same) lock the
* collection metadata and a cursorId, the query will return results for exactly the ranges in
* the metadata (though of arbitrary staleness). This is the sharded collection query contract.
*
* END NOTE FROM GREG
*
* Preconditions: Child must be fetched. TODO: when covering analysis is in just build doc
* and check that against shard key. See SERVER-5022.
*/
class ShardFilterStage final : public PlanStage {
public:
ShardFilterStage(OperationContext* opCtx,
ScopedCollectionMetadata metadata,
WorkingSet* ws,
PlanStage* child);
~ShardFilterStage();
bool isEOF() final;
StageState doWork(WorkingSetID* out) final;
StageType stageType() const final {
return STAGE_SHARDING_FILTER;
}
std::unique_ptr<PlanStageStats> getStats() final;
const SpecificStats* getSpecificStats() const final;
static const char* kStageType;
private:
WorkingSet* _ws;
// Stats
ShardingFilterStats _specificStats;
// Note: it is important that this is the metadata from the time this stage is constructed.
// See class comment for details.
ScopedCollectionMetadata _metadata;
};
} // namespace mongo
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