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/**
* Copyright (C) 2017 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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/document_source.h"
#include "mongo/db/pipeline/document_sources_gen.h"
#include "mongo/db/pipeline/resume_token.h"
namespace mongo {
// Currently the two resume sources take the same specification.
typedef DocumentSourceEnsureResumeTokenPresentSpec DocumentSourceShardCheckResumabilitySpec;
/**
* 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 resume token, 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
* token. 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 DocumentSourceNeedsMongoProcessInterface {
public:
GetNextResult getNext() final;
const char* getSourceName() const final;
StageConstraints constraints() const final {
return {StreamType::kStreaming,
PositionRequirement::kNone,
HostTypeRequirement::kAnyShard,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kNotAllowed};
}
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
static boost::intrusive_ptr<DocumentSourceShardCheckResumability> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
DocumentSourceShardCheckResumabilitySpec spec);
private:
/**
* Use the create static method to create a DocumentSourceShardCheckResumability.
*/
DocumentSourceShardCheckResumability(const boost::intrusive_ptr<ExpressionContext>& expCtx,
DocumentSourceShardCheckResumabilitySpec spec);
ResumeToken _token;
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 SplittableDocumentSource {
public:
GetNextResult getNext() final;
const char* getSourceName() const final;
StageConstraints constraints() const final {
return {StreamType::kStreaming,
PositionRequirement::kNone,
HostTypeRequirement::kNone,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kNotAllowed};
}
/**
* SplittableDocumentSource methods; this has to run on the merger, since the resume point could
* be at any shard.
*/
boost::intrusive_ptr<DocumentSource> getShardSource() final {
DocumentSourceShardCheckResumabilitySpec shardSpec;
shardSpec.setResumeToken(_token);
return DocumentSourceShardCheckResumability::create(pExpCtx, shardSpec);
};
boost::intrusive_ptr<DocumentSource> getMergeSource() final {
return this;
};
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
static boost::intrusive_ptr<DocumentSourceEnsureResumeTokenPresent> create(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
DocumentSourceEnsureResumeTokenPresentSpec spec);
const ResumeToken& getTokenForTest() {
return _token;
}
private:
/**
* Use the create static method to create a DocumentSourceEnsureResumeTokenPresent.
*/
DocumentSourceEnsureResumeTokenPresent(const boost::intrusive_ptr<ExpressionContext>& expCtx,
DocumentSourceEnsureResumeTokenPresentSpec spec);
ResumeToken _token;
bool _seenDoc;
};
} // namespace mongo
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