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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/pipeline/change_stream_constants.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/document_source_change_stream.h"
#include "mongo/db/pipeline/document_source_change_stream_gen.h"
#include "mongo/db/pipeline/document_source_sort.h"
#include "mongo/db/pipeline/resume_token.h"
#include "mongo/db/query/query_knobs.h"
namespace mongo {
/**
* This checks for resumability on a single shard in the sharded case. The rules are
*
* - If the first document in the pipeline for this shard has a matching timestamp, we can
* always resume.
* - If the oplog is empty, we can resume. An empty oplog is rare and can only occur
* on a secondary that has just started up from a primary that has not taken a write.
* In particular, an empty oplog cannot be the result of oplog truncation.
* - If neither of the above is true, the least-recent document in the oplog must precede the resume
* timestamp. If we do this check after seeing the first document in the pipeline in the shard, or
* after seeing that there are no documents in the pipeline after the resume token in the shard,
* we're guaranteed not to miss any documents.
*
* - Otherwise we cannot resume, as we do not know if this shard lost documents between the resume
* token and the first matching document in the pipeline.
*
* This source need only run on a sharded collection. For unsharded collections,
* DocumentSourceEnsureResumeTokenPresent is sufficient.
*/
class DocumentSourceShardCheckResumability final : public DocumentSource {
public:
GetNextResult getNext() final;
const char* getSourceName() const final;
StageConstraints constraints(Pipeline::SplitState pipeState) const final {
return {StreamType::kStreaming,
PositionRequirement::kNone,
HostTypeRequirement::kAnyShard,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kNotAllowed,
TransactionRequirement::kNotAllowed,
ChangeStreamRequirement::kChangeStreamStage};
}
boost::optional<MergingLogic> mergingLogic() final {
return boost::none;
}
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
static boost::intrusive_ptr<DocumentSourceShardCheckResumability> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx, Timestamp ts);
private:
/**
* Use the create static method to create a DocumentSourceShardCheckResumability.
*/
DocumentSourceShardCheckResumability(const boost::intrusive_ptr<ExpressionContext>& expCtx,
Timestamp ts);
Timestamp _resumeTimestamp;
bool _verifiedResumability;
};
/**
* This stage is used internally for change streams to ensure that the resume token is in the
* stream. It is not intended to be created by the user.
*/
class DocumentSourceEnsureResumeTokenPresent final : public DocumentSource {
public:
// Used to record the results of comparing the token data extracted from documents in the
// resumed stream against the client's resume token.
enum class ResumeStatus {
kFoundToken, // The stream produced a document satisfying the client resume token.
kCannotResume, // The stream's latest document is more recent than the resume token.
kCheckNextDoc // The next document produced by the stream may contain the resume token.
};
GetNextResult getNext() final;
const char* getSourceName() const final;
StageConstraints constraints(Pipeline::SplitState) const final {
return {StreamType::kStreaming,
PositionRequirement::kNone,
// If this is parsed on mongos it should stay on mongos. If we're not in a sharded
// cluster then it's okay to run on mongod.
HostTypeRequirement::kLocalOnly,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kNotAllowed,
TransactionRequirement::kNotAllowed,
ChangeStreamRequirement::kChangeStreamStage};
}
boost::optional<MergingLogic> mergingLogic() final {
MergingLogic logic;
// This stage must run on mongos to ensure it sees the resume token, which could have come
// from any shard. We also must include a mergingPresorted $sort stage to communicate to
// the AsyncResultsMerger that we need to merge the streams in a particular order.
logic.mergingStage = this;
// Also add logic to the shards to ensure that each shard has enough oplog history to resume
// the change stream.
logic.shardsStage = DocumentSourceShardCheckResumability::create(
pExpCtx, _tokenFromClient.getClusterTime());
logic.inputSortPattern = change_stream_constants::kSortSpec;
return logic;
};
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
static boost::intrusive_ptr<DocumentSourceEnsureResumeTokenPresent> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx, ResumeToken token);
const ResumeToken& getTokenForTest() {
return _tokenFromClient;
}
private:
/**
* Use the create static method to create a DocumentSourceEnsureResumeTokenPresent.
*/
DocumentSourceEnsureResumeTokenPresent(const boost::intrusive_ptr<ExpressionContext>& expCtx,
ResumeToken token);
ResumeStatus _resumeStatus = ResumeStatus::kCheckNextDoc;
ResumeToken _tokenFromClient;
};
} // namespace mongo
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