SERVER-21154 Batch and parse oplog entries in parallel with applying them

This includes the start of SERVER-21155.

1 files changed, 31 insertions, 9 deletions

diff --git a/src/mongo/db/repl/sync_tail.h b/src/mongo/db/repl/sync_tail.h
index 254f0182bd5..e3edacaed2a 100644
--- a/src/mongo/db/repl/sync_tail.h
+++ b/src/mongo/db/repl/sync_tail.h
@@ -95,38 +95,58 @@ public:
     void oplogApplication();
     bool peek(BSONObj* obj);
 
+    /**
+     * A parsed oplog entry.
+     *
+     * This only includes the fields used by the code using this object at the time this was
+     * written. As more code uses this, more fields should be added.
+     *
+     * All unowned members (such as StringDatas and BSONElements) point into the raw BSON.
+     * All StringData members are guaranteed to be NUL terminated.
+     */
+    struct OplogEntry {
+        explicit OplogEntry(const BSONObj& raw);
+
+        BSONObj raw;  // Owned.
+
+        StringData ns = "";
+        StringData opType = "";
+
+        BSONElement version;
+        BSONElement o;
+        BSONElement o2;
+    };
+
     class OpQueue {
     public:
         OpQueue() : _size(0) {}
         size_t getSize() const {
             return _size;
         }
-        const std::deque<BSONObj>& getDeque() const {
+        const std::deque<OplogEntry>& getDeque() const {
             return _deque;
         }
-        void push_back(BSONObj& op) {
-            _deque.push_back(op);
-            _size += op.objsize();
+        void push_back(OplogEntry&& op) {
+            _size += op.raw.objsize();
+            _deque.push_back(std::move(op));
         }
         bool empty() const {
             return _deque.empty();
         }
 
-        BSONObj back() const {
+        const OplogEntry& back() const {
             invariant(!_deque.empty());
             return _deque.back();
         }
 
     private:
-        std::deque<BSONObj> _deque;
+        std::deque<OplogEntry> _deque;
         size_t _size;
     };
 
     // returns true if we should continue waiting for BSONObjs, false if we should
     // stop waiting and apply the queue we have.  Only returns false if !ops.empty().
-    bool tryPopAndWaitForMore(OperationContext* txn,
-                              OpQueue* ops,
-                              ReplicationCoordinator* replCoord);
+    bool tryPopAndWaitForMore(OperationContext* txn, OpQueue* ops);
 
     /**
      * Fetch a single document referenced in the operation from the sync source.
@@ -158,6 +178,8 @@ protected:
     OpTime multiApply(OperationContext* txn, const OpQueue& ops);
 
 private:
+    class OpQueueBatcher;
+
     std::string _hostname;
 
     BackgroundSyncInterface* _networkQueue;