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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.
*/
#include "mongo/db/pipeline/document_source_change_stream_oplog_match.h"
#include "mongo/bson/bsonmisc.h"
#include "mongo/db/pipeline/change_stream_filter_helpers.h"
#include "mongo/db/pipeline/change_stream_helpers.h"
#include "mongo/db/pipeline/document_source_change_stream_unwind_transaction.h"
namespace mongo {
REGISTER_INTERNAL_DOCUMENT_SOURCE(_internalChangeStreamOplogMatch,
LiteParsedDocumentSourceChangeStreamInternal::parse,
DocumentSourceChangeStreamOplogMatch::createFromBson,
true);
namespace change_stream_filter {
/**
* Produce the MatchExpression representing the filter for the $match stage to filter oplog entries
* to only those relevant for this $changeStream stage.
*
* If there is a 'userMatch' $match stage that will apply to documents generated by the
* $changeStream, this filter can incorporate portions of the predicate, so as to filter out oplog
* entries that would definitely be filtered out by the 'userMatch' filter.
*
* NB: When passing a non-NULL 'userMatch' expression, the resulting expression is built using a
* "shallow clone" of the 'userMatch' (i.e., the result of 'MatchExpression::clone()') and
* can contain references to strings in the BSONObj that 'userMatch' originated from. Callers that
* keep the new filter long-term should serialize and re-parse it to guard against the possibility
* of stale string references.
*/
std::unique_ptr<MatchExpression> buildOplogMatchFilter(
const boost::intrusive_ptr<ExpressionContext>& expCtx,
Timestamp startFromInclusive,
const MatchExpression* userMatch = nullptr) {
tassert(6394401,
"Expected changeStream spec to be present while building the oplog match filter",
expCtx->changeStreamSpec);
// Start building the oplog filter by adding predicates that apply to every entry.
auto oplogFilter = std::make_unique<AndMatchExpression>();
oplogFilter->add(buildTsFilter(expCtx, startFromInclusive, userMatch));
if (!expCtx->changeStreamSpec->getShowMigrationEvents()) {
oplogFilter->add(buildNotFromMigrateFilter(expCtx, userMatch));
}
// Create an $or filter which only captures relevant events in the oplog.
auto eventFilter = std::make_unique<OrMatchExpression>();
eventFilter->add(buildOperationFilter(expCtx, userMatch));
eventFilter->add(buildInvalidationFilter(expCtx, userMatch));
eventFilter->add(buildTransactionFilter(expCtx, userMatch));
eventFilter->add(buildInternalOpFilter(expCtx, userMatch));
// We currently do not support opening a change stream on a view namespace. So we only need to
// add this filter when the change stream type is whole-db or whole cluster.
if (expCtx->changeStreamSpec->getShowExpandedEvents() &&
expCtx->ns.isCollectionlessAggregateNS()) {
eventFilter->add(buildViewDefinitionEventFilter(expCtx, userMatch));
}
// Build the final $match filter to be applied to the oplog.
oplogFilter->add(std::move(eventFilter));
// Perform a final optimization pass on the complete filter before returning.
return MatchExpression::optimize(std::move(oplogFilter));
}
} // namespace change_stream_filter
DocumentSourceChangeStreamOplogMatch::DocumentSourceChangeStreamOplogMatch(
Timestamp clusterTime, const boost::intrusive_ptr<ExpressionContext>& expCtx)
: DocumentSourceMatch(change_stream_filter::buildOplogMatchFilter(expCtx, clusterTime),
expCtx) {
_clusterTime = clusterTime;
expCtx->tailableMode = TailableModeEnum::kTailableAndAwaitData;
}
boost::intrusive_ptr<DocumentSourceChangeStreamOplogMatch>
DocumentSourceChangeStreamOplogMatch::create(const boost::intrusive_ptr<ExpressionContext>& expCtx,
const DocumentSourceChangeStreamSpec& spec) {
auto resumeToken = change_stream::resolveResumeTokenFromSpec(expCtx, spec);
return make_intrusive<DocumentSourceChangeStreamOplogMatch>(resumeToken.clusterTime, expCtx);
}
boost::intrusive_ptr<DocumentSource> DocumentSourceChangeStreamOplogMatch::createFromBson(
BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx) {
uassert(5467600,
"the match filter must be an expression in an object",
elem.type() == BSONType::Object);
auto parsedSpec = DocumentSourceChangeStreamOplogMatchSpec::parse(
IDLParserContext("DocumentSourceChangeStreamOplogMatchSpec"), elem.Obj());
// Note: raw new used here to access private constructor.
return new DocumentSourceChangeStreamOplogMatch(parsedSpec.getFilter(), pExpCtx);
}
const char* DocumentSourceChangeStreamOplogMatch::getSourceName() const {
// This is used in error reporting, particularly if we find this stage in a position other
// than first, so report the name as $changeStream.
return kStageName.rawData();
}
StageConstraints DocumentSourceChangeStreamOplogMatch::constraints(
Pipeline::SplitState pipeState) const {
StageConstraints constraints(StreamType::kStreaming,
PositionRequirement::kFirst,
HostTypeRequirement::kAnyShard,
DiskUseRequirement::kNoDiskUse,
FacetRequirement::kNotAllowed,
TransactionRequirement::kNotAllowed,
LookupRequirement::kNotAllowed,
UnionRequirement::kNotAllowed,
ChangeStreamRequirement::kChangeStreamStage);
constraints.isIndependentOfAnyCollection =
pExpCtx->ns.isCollectionlessAggregateNS() ? true : false;
return constraints;
}
Pipeline::SourceContainer::iterator DocumentSourceChangeStreamOplogMatch::doOptimizeAt(
Pipeline::SourceContainer::iterator itr, Pipeline::SourceContainer* container) {
tassert(5687203, "Iterator mismatch during optimization", *itr == this);
auto nextChangeStreamStageItr = std::next(itr);
// (Ignore FCV check): This feature flag doesn't have upgrade/downgrade concern.
if (!feature_flags::gFeatureFlagChangeStreamsRewrite.isEnabledAndIgnoreFCVUnsafe()) {
return nextChangeStreamStageItr;
}
// It is not safe to combine any parts of a user $match with this stage when the $user match has
// a non-simple collation, because this stage's MatchExpression always executes wtih the simple
// collation.
if (pExpCtx->getCollator()) {
return nextChangeStreamStageItr;
}
// Seek to the stage that immediately follows the change streams stages.
itr = std::find_if_not(itr, container->end(), [](const auto& stage) {
return stage->constraints().isChangeStreamStage();
});
// Optimize the pipeline after this stage to merge $match stages and push them forward. Note, if
// we have already performed the '_optimizedEndOfPipeline' step, we assume that we have also
// applied any $match rewrites that would be available to this function and that no further
// optimization is necessary. The optimizations in this function are not designed to be
// attempted multiple times.
if (_optimizedEndOfPipeline) {
return itr;
}
itr = Pipeline::optimizeEndOfPipeline(std::prev(itr), container);
_optimizedEndOfPipeline = true;
if (itr == container->end()) {
// This pipeline is just the change stream.
return itr;
}
auto matchStage = dynamic_cast<DocumentSourceMatch*>(itr->get());
if (!matchStage) {
// This function only attempts to optimize a $match that immediately follows expanded
// $changeStream stages. That does not apply here, and we resume optimization at the last
// change stream stage, in case a "swap" optimization can apply between it and the stage
// that follows it. For example, $project stages can swap in front of the last change stream
// stages.
return std::prev(itr);
}
tassert(5687204, "Attempt to rewrite an interalOplogMatch after deserialization", _clusterTime);
// Recreate the change stream filter with additional predicates from the user's $match.
auto filterWithUserPredicates = change_stream_filter::buildOplogMatchFilter(
pExpCtx, *_clusterTime, matchStage->getMatchExpression());
// Set the internal DocumentSourceMatch state to the new filter.
rebuild(filterWithUserPredicates->serialize());
// Continue optimization at the next change stream stage.
return nextChangeStreamStageItr;
}
Value DocumentSourceChangeStreamOplogMatch::serialize(SerializationOptions opts) const {
BSONObjBuilder builder;
if (opts.verbosity) {
BSONObjBuilder sub(builder.subobjStart(DocumentSourceChangeStream::kStageName));
sub.append("stage"_sd, kStageName);
sub.append(DocumentSourceChangeStreamOplogMatchSpec::kFilterFieldName,
getMatchExpression()->serialize(opts));
sub.done();
} else {
BSONObjBuilder sub(builder.subobjStart(kStageName));
if (opts.replacementForLiteralArgs || opts.applyHmacToIdentifiers) {
sub.append(DocumentSourceChangeStreamOplogMatchSpec::kFilterFieldName,
getMatchExpression()->serialize(opts));
} else {
DocumentSourceChangeStreamOplogMatchSpec(_predicate).serialize(&sub);
}
sub.done();
}
return Value(builder.obj());
}
} // namespace mongo
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