SERVER-65154 Create write listeners/controllers per collection that track ‘Change’ diffs

1 files changed, 90 insertions, 0 deletions

diff --git a/src/mongo/db/catalog/derived_metadata_collection_count.cpp b/src/mongo/db/catalog/derived_metadata_collection_count.cpp
new file mode 100644
index 00000000000..e7ea5f942b4
--- /dev/null
+++ b/src/mongo/db/catalog/derived_metadata_collection_count.cpp
@@ -0,0 +1,90 @@
+/**
+ *    Copyright (C) 2022-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/catalog/derived_metadata_collection_count.h"
+
+#include "mongo/bson/bsonobj.h"
+
+namespace mongo {
+const auto getDerivedCountDecoration =
+    SharedCollectionDecorations::declareDecoration<DerivedMetadataCount>();
+
+DerivedMetadataCount& DerivedMetadataCount::get(const Collection* coll) {
+    return getDerivedCountDecoration(coll->getSharedDecorations());
+}
+
+std::pair<Timestamp, long long> DerivedMetadataCount::getLatestValue() {
+    stdx::lock_guard lock(_valueMutex);
+    return _latestTimestampedValue;
+}
+
+void DerivedMetadataCount::populateDelta(const DocumentWriteImages& write,
+                                         DerivedMetadataDelta* delta) {
+    if (write.documentPreImage.isEmpty() && !write.documentPostImage.isEmpty()) {
+        // Inserting a document so increment the count.
+        delta->countUpdate = 1;
+    } else if (!write.documentPreImage.isEmpty() && write.documentPostImage.isEmpty()) {
+        // Deleting a document so decrement the count.
+        delta->countUpdate = -1;
+    } else {
+        delta->countUpdate = 0;
+    }
+}
+
+void DerivedMetadataCount::applyDeltas(const std::vector<DerivedMetadataDelta>& deltas) {
+    stdx::lock_guard lock(_valueMutex);
+    const auto& latestTimestamp = _latestTimestampedValue.first;
+    long long deltaSum = _latestTimestampedValue.second;
+
+    Timestamp newMaxTimestamp = Timestamp(0);
+    for (auto& delta : deltas) {
+        // Ignore Deltas with Timestamps less than or equal to the latest Timestamp.
+        if (delta.timestamp <= latestTimestamp) {
+            continue;
+        }
+        newMaxTimestamp = (newMaxTimestamp < delta.timestamp) ? delta.timestamp : newMaxTimestamp;
+        deltaSum += delta.countUpdate;
+    }
+
+    // If none of the Deltas were new, we can skip updating the latest value.
+    if (newMaxTimestamp <= latestTimestamp) {
+        return;
+    }
+
+    _updateLatestValue(lock, std::move(newMaxTimestamp), deltaSum);
+}
+
+void DerivedMetadataCount::_updateLatestValue(WithLock,
+                                              Timestamp newTimestamp,
+                                              long long newCount) {
+    _latestTimestampedValue = {std::move(newTimestamp), newCount};
+}
+}  // namespace mongo