SERVER-24817 Make ShardLocal wait for writes it performed when doing majority reads

This reverts commit ed19a4a874a7ed792a850c71e352eee2f2bb167c.

1 files changed, 27 insertions, 0 deletions

diff --git a/src/mongo/s/client/shard_local.h b/src/mongo/s/client/shard_local.h
index b39aba621d0..449a5d7a037 100644
--- a/src/mongo/s/client/shard_local.h
+++ b/src/mongo/s/client/shard_local.h
@@ -30,7 +30,9 @@
 
 #include "mongo/base/disallow_copying.h"
 #include "mongo/client/dbclientinterface.h"
+#include "mongo/db/repl/optime.h"
 #include "mongo/s/client/shard.h"
+#include "mongo/stdx/mutex.h"
 
 namespace mongo {
 
@@ -75,6 +77,31 @@ private:
         const BSONObj& query,
         const BSONObj& sort,
         boost::optional<long long> limit) final;
+
+    /**
+     * Checks if an OpTime was set on the current Client (ie if the current operation performed a
+     * write) and if so updates _lastOpTime to the OpTime from the write that was just performed.
+     * The 'previousOpTimeOnClient' parameter is the optime that *was* the optime on this client
+     * before we ran this command through this ShardLocal.  By the time this method is called,
+     * if the optime set on the Client is different than 'previousOpTimeOnClient' then that means
+     * the command just run did a write and we should update _lastOpTime to capture the optime of
+     * the write we just did.  If the current optime on the client is the same as
+     * 'previousOpTimeOnClient' then the command we just ran didn't do a write, and we should leave
+     * _lastOpTime alone.
+     */
+    void _updateLastOpTimeFromClient(OperationContext* txn,
+                                     const repl::OpTime& previousOpTimeOnClient);
+
+    repl::OpTime _getLastOpTime();
+
+    // Guards _lastOpTime below.
+    stdx::mutex _mutex;
+
+    // Stores the optime that was generated by the last operation to perform a write that was run
+    // through _runCommand.  Used in _exhaustiveFindOnConfig for waiting for that optime to be
+    // committed so that readConcern majority reads will read the writes that were performed without
+    // a w:majority write concern.
+    repl::OpTime _lastOpTime{};
 };
 
 }  // namespace mongo