SERVER-48717 Implement the persist/recover functionalities of the VectorClock

1 files changed, 26 insertions, 0 deletions

diff --git a/src/mongo/db/vector_clock.h b/src/mongo/db/vector_clock.h
index 6434cd3aa6b..750f3a9133c 100644
--- a/src/mongo/db/vector_clock.h
+++ b/src/mongo/db/vector_clock.h
@@ -31,11 +31,14 @@
 
 #include <array>
 
+#include "mongo/client/query.h"
 #include "mongo/db/logical_time.h"
 #include "mongo/db/operation_context.h"
 #include "mongo/db/service_context.h"
+#include "mongo/db/vector_clock_document_gen.h"
 #include "mongo/platform/mutex.h"
 #include "mongo/transport/session.h"
+#include "mongo/util/static_immortal.h"
 
 namespace mongo {
 
@@ -132,9 +135,32 @@ public:
      */
     bool isEnabled() const;
 
+    /*
+     * Methods to save/recover the the vector clock to/from persistent storage. Subclasses are
+     * eventually expected to override those method to provide persistence mechanisms. Default
+     * implementations result in a NOP.
+     */
+    virtual SharedSemiFuture<void> persist(OperationContext* opCtx) {
+        return SharedSemiFuture<void>();
+    }
+    virtual SharedSemiFuture<void> recover(OperationContext* opCtx) {
+        return SharedSemiFuture<void>();
+    }
+    virtual void waitForInMemoryVectorClockToBePersisted(OperationContext* opCtx) {}
+    virtual void waitForVectorClockToBeRecovered(OperationContext* opCtx){};
+
     void resetVectorClock_forTest();
     void advanceTime_forTest(Component component, LogicalTime newTime);
 
+    // Query to use when reading/writing the vector clock state document.
+    static const Query& kStateQuery() {
+        static StaticImmortal<Query> q{QUERY(VectorClockDocument::k_idFieldName << kDocIdKey)};
+        return *q;
+    }
+
+    // The _id value of the vector clock singleton document.
+    static constexpr StringData kDocIdKey = "vectorClockState"_sd;
+
 protected:
     class ComponentFormat {