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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.
*/
#include "mongo/platform/basic.h"
#include "mongo/db/exec/change_stream_proxy.h"
#include "mongo/db/pipeline/pipeline_d.h"
#include "mongo/db/pipeline/resume_token.h"
#include "mongo/db/repl/speculative_majority_read_info.h"
namespace mongo {
const char* ChangeStreamProxyStage::kStageType = "CHANGE_STREAM_PROXY";
ChangeStreamProxyStage::ChangeStreamProxyStage(OperationContext* opCtx,
std::unique_ptr<Pipeline, PipelineDeleter> pipeline,
WorkingSet* ws)
: PipelineProxyStage(opCtx, std::move(pipeline), ws, kStageType) {
// Set _postBatchResumeToken to the initial PBRT that was added to the expression context during
// pipeline construction, and use it to obtain the starting time for _latestOplogTimestamp.
invariant(!_pipeline->getContext()->initialPostBatchResumeToken.isEmpty());
_postBatchResumeToken = _pipeline->getContext()->initialPostBatchResumeToken.getOwned();
if (!_pipeline->getContext()->needsMerge || _pipeline->getContext()->mergeByPBRT) {
_latestOplogTimestamp = ResumeToken::parse(_postBatchResumeToken).getData().clusterTime;
}
}
boost::optional<BSONObj> ChangeStreamProxyStage::getNextBson() {
if (auto next = _pipeline->getNext()) {
// While we have more results to return, we track both the timestamp and the resume token of
// the latest event observed in the oplog, the latter via its sort key metadata field.
auto nextBSON = _validateAndConvertToBSON(*next);
_latestOplogTimestamp = PipelineD::getLatestOplogTimestamp(_pipeline.get());
_postBatchResumeToken = next->getSortKeyMetaField();
_setSpeculativeReadTimestamp();
return nextBSON;
}
// We ran out of results to return. Check whether the oplog cursor has moved forward since the
// last recorded timestamp. Because we advance _latestOplogTimestamp for every event we return,
// if the new time is higher than the last then we are guaranteed not to have already returned
// any events at this timestamp. We can set _postBatchResumeToken to a new high-water-mark token
// at the current clusterTime.
auto highWaterMark = PipelineD::getLatestOplogTimestamp(_pipeline.get());
if (highWaterMark > _latestOplogTimestamp) {
auto token = ResumeToken::makeHighWaterMarkToken(highWaterMark);
_postBatchResumeToken = token.toDocument().toBson();
_latestOplogTimestamp = highWaterMark;
_setSpeculativeReadTimestamp();
}
return boost::none;
}
BSONObj ChangeStreamProxyStage::_validateAndConvertToBSON(const Document& event) const {
// If we are producing output to be merged on mongoS, then no stages can have modified the _id.
if (_includeMetaData) {
return event.toBsonWithMetaData();
}
// Confirm that the document _id field matches the original resume token in the sort key field.
auto eventBSON = event.toBson();
auto resumeToken = event.getSortKeyMetaField();
auto idField = eventBSON.getObjectField("_id");
invariant(!resumeToken.isEmpty());
uassert(ErrorCodes::ChangeStreamFatalError,
str::stream() << "Encountered an event whose _id field, which contains the resume "
"token, was modified by the pipeline. Modifying the _id field of an "
"event makes it impossible to resume the stream from that point. Only "
"transformations that retain the unmodified _id field are allowed. "
"Expected: "
<< BSON("_id" << resumeToken)
<< " but found: "
<< (eventBSON["_id"] ? BSON("_id" << eventBSON["_id"]) : BSONObj()),
idField.binaryEqual(resumeToken));
return eventBSON;
}
void ChangeStreamProxyStage::_setSpeculativeReadTimestamp() {
repl::SpeculativeMajorityReadInfo& speculativeMajorityReadInfo =
repl::SpeculativeMajorityReadInfo::get(_pipeline->getContext()->opCtx);
if (speculativeMajorityReadInfo.isSpeculativeRead() && !_latestOplogTimestamp.isNull()) {
speculativeMajorityReadInfo.setSpeculativeReadTimestampForward(_latestOplogTimestamp);
}
}
std::unique_ptr<PlanStageStats> ChangeStreamProxyStage::getStats() {
std::unique_ptr<PlanStageStats> ret =
std::make_unique<PlanStageStats>(CommonStats(kStageType), STAGE_CHANGE_STREAM_PROXY);
ret->specific = std::make_unique<CollectionScanStats>();
return ret;
}
} // namespace mongo
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