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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/pipeline/document_source_sample.h"
#include "mongo/db/client.h"
#include "mongo/db/pipeline/document.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/expression_context.h"
#include "mongo/db/pipeline/lite_parsed_document_source.h"
#include "mongo/db/pipeline/value.h"
namespace mongo {
using boost::intrusive_ptr;
constexpr StringData DocumentSourceSample::kStageName;
DocumentSourceSample::DocumentSourceSample(const intrusive_ptr<ExpressionContext>& pExpCtx)
: DocumentSource(pExpCtx), _size(0) {}
REGISTER_DOCUMENT_SOURCE(sample,
LiteParsedDocumentSourceDefault::parse,
DocumentSourceSample::createFromBson);
DocumentSource::GetNextResult DocumentSourceSample::getNext() {
if (_size == 0)
return GetNextResult::makeEOF();
pExpCtx->checkForInterrupt();
if (!_sortStage->isPopulated()) {
// Exhaust source stage, add random metadata, and push all into sorter.
PseudoRandom& prng = pExpCtx->opCtx->getClient()->getPrng();
auto nextInput = pSource->getNext();
for (; nextInput.isAdvanced(); nextInput = pSource->getNext()) {
MutableDocument doc(nextInput.releaseDocument());
doc.setRandMetaField(prng.nextCanonicalDouble());
_sortStage->loadDocument(doc.freeze());
}
switch (nextInput.getStatus()) {
case GetNextResult::ReturnStatus::kAdvanced: {
MONGO_UNREACHABLE; // We consumed all advances above.
}
case GetNextResult::ReturnStatus::kPauseExecution: {
return nextInput; // Propagate the pause.
}
case GetNextResult::ReturnStatus::kEOF: {
_sortStage->loadingDone();
}
}
}
invariant(_sortStage->isPopulated());
return _sortStage->getNext();
}
Value DocumentSourceSample::serialize(boost::optional<ExplainOptions::Verbosity> explain) const {
return Value(DOC(kStageName << DOC("size" << _size)));
}
namespace {
const BSONObj randSortSpec = BSON("$rand" << BSON("$meta"
<< "randVal"));
} // namespace
intrusive_ptr<DocumentSource> DocumentSourceSample::createFromBson(
BSONElement specElem, const intrusive_ptr<ExpressionContext>& expCtx) {
uassert(28745, "the $sample stage specification must be an object", specElem.type() == Object);
intrusive_ptr<DocumentSourceSample> sample(new DocumentSourceSample(expCtx));
bool sizeSpecified = false;
for (auto&& elem : specElem.embeddedObject()) {
auto fieldName = elem.fieldNameStringData();
if (fieldName == "size") {
uassert(28746, "size argument to $sample must be a number", elem.isNumber());
uassert(28747, "size argument to $sample must not be negative", elem.numberLong() >= 0);
sample->_size = elem.numberLong();
sizeSpecified = true;
} else {
uasserted(28748, str::stream() << "unrecognized option to $sample: " << fieldName);
}
}
uassert(28749, "$sample stage must specify a size", sizeSpecified);
sample->_sortStage = DocumentSourceSort::create(expCtx, randSortSpec, sample->_size);
return sample;
}
boost::optional<DocumentSource::MergingLogic> DocumentSourceSample::mergingLogic() {
// On the merger we need to merge the pre-sorted documents by their random values, then limit to
// the number we need.
MergingLogic logic;
logic.shardsStage = this;
if (_size > 0) {
logic.mergingStage = DocumentSourceLimit::create(pExpCtx, _size);
}
// Here we don't use 'randSortSpec' because it uses a metadata sort which the merging logic does
// not understand. The merging logic will use the serialized sort key, and this sort pattern is
// just used to communicate ascending/descending information. A pattern like {$meta: "randVal"}
// is neither ascending nor descending, and so will not be useful when constructing the merging
// logic.
logic.inputSortPattern = BSON("$rand" << -1);
return logic;
}
} // namespace mongo
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