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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/document_source_change_stream.h"
namespace mongo {
/**
* This stage keeps track of applyOps oplog entries that represent transactions and "unwinds" them
* whenever an oplog entry commits a transaction. When the stage observes an applyOps or commit
* command that commits a transaction, it emits one document for each operation in the transaction
* that matches the namespace filter. The applyOps entries themselves are removed from the stage's
* output, but all other entries pass through unmodified. Note that the namespace filter applies
* only to unwound transaction operations, not to any other entries.
*/
class DocumentSourceChangeStreamUnwindTransaction : public DocumentSource,
public ChangeStreamStageSerializationInterface {
public:
static constexpr StringData kStageName = "$_internalChangeStreamUnwindTransaction"_sd;
static boost::intrusive_ptr<DocumentSourceChangeStreamUnwindTransaction> create(
const boost::intrusive_ptr<ExpressionContext>&);
static boost::intrusive_ptr<DocumentSourceChangeStreamUnwindTransaction> createFromBson(
const BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& expCtx);
DepsTracker::State getDependencies(DepsTracker* deps) const final;
DocumentSource::GetModPathsReturn getModifiedPaths() const final;
Value serialize(boost::optional<ExplainOptions::Verbosity> explain) const {
return ChangeStreamStageSerializationInterface::serializeToValue(explain);
}
Value serializeLegacy(boost::optional<ExplainOptions::Verbosity> explain) const;
Value serializeLatest(boost::optional<ExplainOptions::Verbosity> explain) const;
StageConstraints constraints(Pipeline::SplitState pipeState) const final;
boost::optional<DistributedPlanLogic> distributedPlanLogic() final {
return boost::none;
}
const char* getSourceName() const {
return DocumentSourceChangeStreamUnwindTransaction::kStageName.rawData();
}
protected:
DocumentSource::GetNextResult doGetNext() override;
private:
DocumentSourceChangeStreamUnwindTransaction(
std::string nsRegex, const boost::intrusive_ptr<ExpressionContext>& expCtx);
/**
* Validates if the supplied document contains transaction details.
*/
bool _isTransactionOplogEntry(const Document& doc);
/**
* Represents the DocumentSource's state if it's currently reading from a transaction.
* Transaction operations are packed into 'applyOps' entries in the oplog.
*
* This iterator returns operations from a transaction that are relevant to the change stream in
* the same order they appear on the oplog (chronological order). Note that the
* TransactionHistoryIterator, which this class uses to query the oplog, returns the oplog
* entries in _reverse_ order. We internally reverse the output of the
* TransactionHistoryIterator in order to get the desired order.
*
* Note that our view of a transaction in the oplog is like an array of arrays with an "outer"
* array of applyOps entries represented by the 'txnOplogEntries' field and "inner" arrays of
* applyOps entries. Each applyOps entry gets loaded on demand, with only a single applyOps
* loaded into '_applyOpsValue' and '_currentApplyOps' at any time.
*
* Likewise, there are "outer" and "inner" iterators, 'txnOplogEntriesIt' and
* '_currentApplyOpsIt' respectively, that together reference the current transaction operation.
*/
class TransactionOpIterator {
public:
TransactionOpIterator(const TransactionOpIterator&) = delete;
TransactionOpIterator& operator=(const TransactionOpIterator&) = delete;
TransactionOpIterator(OperationContext* opCtx,
std::shared_ptr<MongoProcessInterface> mongoProcessInterface,
const Document& input,
const pcrecpp::RE& nsRegex);
/**
* Returns the index for the last operation returned by getNextTransactionOp(). It is
* illegal to call this before calling getNextTransactionOp() at least once.
*/
size_t txnOpIndex() const {
// 'txnOpIndex' points to the _next_ transaction index, so we must subtract one to get
// the index of the entry being examined right now.
invariant(_txnOpIndex >= 1);
return _txnOpIndex - 1;
}
Timestamp clusterTime() const {
return _clusterTime;
}
Document lsid() const {
return _lsid;
}
TxnNumber txnNumber() const {
return _txnNumber;
}
/**
* Extract one Document from the transaction and advance the iterator. Returns boost::none
* to indicate that there are no operations left.
*/
boost::optional<Document> getNextTransactionOp(OperationContext* opCtx);
private:
// Perform a find on the oplog to find an OplogEntry by its OpTime.
repl::OplogEntry _lookUpOplogEntryByOpTime(OperationContext* opCtx,
repl::OpTime lookupTime) const;
// Helper for getNextTransactionOp(). Checks the namespace of the given document to see if
// it should be returned in the change stream.
bool _isDocumentRelevant(const Document& d) const;
// Traverse backwards through the oplog by starting at the entry at 'firstOpTime' and
// following "prevOpTime" links until reaching the terminal "prevOpTime" value, and push the
// OpTime value to '_txnOplogEntries' for each entry traversed, including the 'firstOpTime'
// entry. Note that we follow the oplog links _backwards_ through the oplog (i.e., in
// reverse chronological order) but because this is a stack, the iterator will process them
// in the opposite order, allowing iteration to proceed fowards and return operations in
// chronological order.
void _collectAllOpTimesFromTransaction(OperationContext* opCtx, repl::OpTime firstOpTime);
// Adds more transaction related information to the document containing unwinded
// transaction.
Document _addRequiredTransactionFields(const Document& doc);
// This stack contains the timestamps for all oplog entries in this transaction that have
// yet to be processed by the iterator. Each time the TransactionOpIterator finishes
// iterating the contents of the '_currentApplyOps' array, it pops an entry off the stack
// and uses it to load the next applyOps entry in the '_currentApplyOps' array, meaning that
// the top entry is always the next entry to be processed. From top-to-bottom, the stack is
// ordered chronologically, in the same order as entries appear in the oplog.
std::stack<repl::OpTime> _txnOplogEntries;
// The '_currentapplyOps' stores the applyOps array that the TransactionOpIterator is
// currently iterating.
Value _currentApplyOps;
// This iterator references the next operation within the '_currentApplyOps' array that the
// the getNextTransactionOp() method will return. When there are no more operations to
// iterate, this iterator will point to the array's "end" sentinel, and '_txnOplogEntries'
// will be empty.
typename std::vector<Value>::const_iterator _currentApplyOpsIt;
// Our current place within the entire transaction, which may consist of multiple 'applyOps'
// arrays.
size_t _txnOpIndex;
// The clusterTime of the _applyOps.
Timestamp _clusterTime;
// Fields that were taken from the '_applyOps' oplog entry.
Document _lsid;
TxnNumber _txnNumber;
// Used for traversing the oplog with TransactionHistoryInterface.
std::shared_ptr<MongoProcessInterface> _mongoProcessInterface;
// An operation is relevant to a change stream iff its namespace matches this regex.
const pcrecpp::RE& _nsRegex;
};
// Regex for matching the "ns" field in applyOps sub-entries. Only used when we have a
// change stream on the entire DB. When watching just a single collection, this field is
// boost::none, and an exact string equality check is used instead.
boost::optional<pcrecpp::RE> _nsRegex;
// Represents the current transaction we're unwinding, if any.
boost::optional<TransactionOpIterator> _txnIterator;
};
} // namespace mongo
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