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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_sequential_document_cache.h"
#include "mongo/db/pipeline/document_source_match.h"
namespace mongo {
constexpr StringData DocumentSourceSequentialDocumentCache::kStageName;
DocumentSourceSequentialDocumentCache::DocumentSourceSequentialDocumentCache(
const boost::intrusive_ptr<ExpressionContext>& expCtx, SequentialDocumentCache* cache)
: DocumentSource(expCtx), _cache(cache) {
invariant(_cache);
invariant(!_cache->isAbandoned());
if (_cache->isServing()) {
_cache->restartIteration();
}
}
DocumentSource::GetNextResult DocumentSourceSequentialDocumentCache::getNext() {
// Either we're reading from the cache, or we have an input source to build the cache from.
invariant(pSource || _cache->isServing());
pExpCtx->checkForInterrupt();
if (_cache->isServing()) {
auto nextDoc = _cache->getNext();
return (nextDoc ? std::move(*nextDoc) : GetNextResult::makeEOF());
}
auto nextResult = pSource->getNext();
if (!_cache->isAbandoned()) {
if (nextResult.isEOF()) {
_cache->freeze();
} else {
_cache->add(nextResult.getDocument());
}
}
return nextResult;
}
Pipeline::SourceContainer::iterator DocumentSourceSequentialDocumentCache::doOptimizeAt(
Pipeline::SourceContainer::iterator itr, Pipeline::SourceContainer* container) {
// The DocumentSourceSequentialDocumentCache should always be the last stage in the pipeline
// pre-optimization. By the time optimization reaches this point, all preceding stages are in
// the final positions which they would have occupied if no cache stage was present.
invariant(_hasOptimizedPos || std::next(itr) == container->end());
invariant((*itr).get() == this);
// If we have already optimized our position, stay where we are.
if (_hasOptimizedPos) {
return std::next(itr);
}
// Mark this stage as having optimized itself.
_hasOptimizedPos = true;
// If the cache is the only stage in the pipeline, return immediately.
if (itr == container->begin()) {
return container->end();
}
// Pop the cache stage off the back of the pipeline.
auto cacheStage = std::move(*itr);
container->erase(itr);
// Get all variable IDs defined in this scope.
auto varIDs = pExpCtx->variablesParseState.getDefinedVariableIDs();
auto prefixSplit = container->begin();
DepsTracker deps;
// Iterate through the pipeline stages until we find one which references an external variable.
for (; prefixSplit != container->end(); ++prefixSplit) {
if (((*prefixSplit)->getDependencies(&deps) ==
DocumentSource::GetDepsReturn::NOT_SUPPORTED) ||
deps.hasVariableReferenceTo(varIDs)) {
break;
}
}
// The 'prefixSplit' iterator is now pointing to the first stage of the correlated suffix. If
// the split point is the first stage, then the entire pipeline is correlated and we should not
// attempt to perform any caching. Abandon the cache and return.
if (prefixSplit == container->begin()) {
_cache->abandon();
return container->end();
}
// If the cache has been populated and is serving results, remove the non-correlated prefix.
if (_cache->isServing()) {
container->erase(container->begin(), prefixSplit);
}
container->insert(prefixSplit, std::move(cacheStage));
return container->end();
}
Value DocumentSourceSequentialDocumentCache::serialize(
boost::optional<ExplainOptions::Verbosity> explain) const {
if (explain) {
return Value(Document{
{kStageName,
Document{{"maxSizeBytes"_sd, Value(static_cast<long long>(_cache->maxSizeBytes()))},
{"status"_sd,
_cache->isBuilding() ? "kBuilding"_sd : _cache->isServing()
? "kServing"_sd
: "kAbandoned"_sd}}}});
}
return Value();
}
} // namesace mongo
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