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/**
* Copyright (C) 2021-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_gen.h"
namespace mongo {
/**
* This stage checks whether or not the oplog has enough history to resume the stream, and consumes
* all events up to the given resume point. It is deployed on all shards when resuming a stream on
* a sharded cluster, and is also used in the single-replicaset case when a stream is opened with
* startAtOperationTime or with a high-water-mark resume token. It defers to the COLLSCAN to check
* whether the first event (matching or non-matching) encountered in the oplog has a timestamp equal
* to or earlier than the minTs in the change stream filter. If not, the COLLSCAN will throw an
* assertion, which this stage catches and converts into a more comprehensible $changeStream
* specific exception. The rules are:
*
* - If the first event seen in the oplog has the same timestamp as the requested resume token or
* startAtOperationTime, we can resume.
* - If the timestamp of the first event seen in the oplog is earlier than the requested resume
* token or startAtOperationTime, we can resume.
* - If the first entry in the oplog is a replica set initialization, then we can resume even if the
* token timestamp is earlier, since no events can have fallen off this oplog yet. This can happen
* in a sharded cluster when a new shard is added.
*
* - Otherwise we cannot resume, as we do not know if there were any events between the resume token
* and the first matching document in the oplog.
*/
class DocumentSourceChangeStreamCheckResumability : public DocumentSource {
public:
static constexpr StringData kStageName = "$_internalChangeStreamCheckResumability"_sd;
// 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.
kSurpassedToken, // 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.
kNeedsSplit // We found a candidate resume token but the event must be split.
};
const char* getSourceName() const override;
StageConstraints constraints(Pipeline::SplitState pipeState) const override {
return {StreamType::kStreaming,
PositionRequirement::kNone,
HostTypeRequirement::kAnyShard,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kNotAllowed,
TransactionRequirement::kNotAllowed,
LookupRequirement::kNotAllowed,
UnionRequirement::kNotAllowed,
ChangeStreamRequirement::kChangeStreamStage};
}
boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
return boost::none;
}
Value serialize(SerializationOptions opts = SerializationOptions()) const override;
void addVariableRefs(std::set<Variables::Id>* refs) const final {}
static boost::intrusive_ptr<DocumentSourceChangeStreamCheckResumability> createFromBson(
BSONElement spec, const boost::intrusive_ptr<ExpressionContext>& expCtx);
static boost::intrusive_ptr<DocumentSourceChangeStreamCheckResumability> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
const DocumentSourceChangeStreamSpec& spec);
static ResumeStatus compareAgainstClientResumeToken(const Document& eventFromResumedStream,
const ResumeTokenData& tokenDataFromClient);
protected:
/**
* Use the create static method to create a DocumentSourceChangeStreamCheckResumability.
*/
DocumentSourceChangeStreamCheckResumability(
const boost::intrusive_ptr<ExpressionContext>& expCtx, ResumeTokenData token);
GetNextResult doGetNext() override;
ResumeStatus _resumeStatus = ResumeStatus::kCheckNextDoc;
const ResumeTokenData _tokenFromClient;
};
} // namespace mongo
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