SERVER-30399 Add caching for $lookup non-correlated sub-pipeline prefix

1 files changed, 88 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/sequential_document_cache.cpp b/src/mongo/db/pipeline/sequential_document_cache.cpp
new file mode 100644
index 00000000000..93d95c0e072
--- /dev/null
+++ b/src/mongo/db/pipeline/sequential_document_cache.cpp
@@ -0,0 +1,88 @@
+/**
+ * Copyright (C) 2017 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * 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
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * 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 GNU Affero General 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/sequential_document_cache.h"
+
+#include "mongo/base/error_codes.h"
+#include "mongo/base/status.h"
+
+namespace mongo {
+
+void SequentialDocumentCache::add(Document doc) {
+    invariant(_status == CacheStatus::kBuilding);
+
+    if (checkCacheSize(doc) != CacheStatus::kAbandoned) {
+        _sizeBytes += doc.getApproximateSize();
+        _cache.push_back(std::move(doc));
+    }
+}
+
+void SequentialDocumentCache::freeze() {
+    invariant(_status == CacheStatus::kBuilding);
+
+    _status = CacheStatus::kServing;
+    _cache.shrink_to_fit();
+
+    _cacheIter = _cache.begin();
+}
+
+void SequentialDocumentCache::abandon() {
+    _status = CacheStatus::kAbandoned;
+
+    _cache.clear();
+    _cache.shrink_to_fit();
+
+    _cacheIter = _cache.begin();
+}
+
+boost::optional<Document> SequentialDocumentCache::getNext() {
+    invariant(_status == CacheStatus::kServing);
+
+    if (_cacheIter == _cache.end()) {
+        return boost::none;
+    }
+
+    return *_cacheIter++;
+}
+
+void SequentialDocumentCache::restartIteration() {
+    invariant(_status == CacheStatus::kServing);
+    _cacheIter = _cache.begin();
+}
+
+SequentialDocumentCache::CacheStatus SequentialDocumentCache::checkCacheSize(const Document& doc) {
+    if (_sizeBytes + doc.getApproximateSize() > _maxSizeBytes) {
+        abandon();
+    }
+
+    return _status;
+}
+
+}  // namespace mongo