diff --git a/db/dur.cpp b/db/dur.cpp
index 9cf79ac80c3..916668f3f69 100644
--- a/db/dur.cpp
+++ b/db/dur.cpp
@@ -193,6 +193,11 @@ namespace mongo {
             return p;
         }
 
+        void DurableImpl::commitIfNeeded() {
+            if (commitJob.bytes() > 50*1024*1024) // should this also fire if CmdLine::DurAlwaysCommit?
+                groupCommit();
+        }
+
         /** Used in _DEBUG builds to check that we didn't overwrite the last intent
             that was declared.  called just before writelock release.  we check a few
             bytes after the declared region to see if they changed.
diff --git a/db/dur.h b/db/dur.h
index 5b666b39bcc..bc6350d82a7 100644
--- a/db/dur.h
+++ b/db/dur.h
@@ -75,6 +75,15 @@ namespace mongo {
             */
             virtual bool commitNow() = 0;
 
+            /** Commit if enough bytes have been modified. Current threshold is 50MB
+
+                The idea is that long running write operations that dont yield
+                (like creating an index or update with $atomic) can call this
+                whenever the db is in a sane state and it will prevent commits
+                from growing too large.
+            */
+            virtual void commitIfNeeded() = 0;
+
 #if defined(_DEBUG)
             virtual void debugCheckLastDeclaredWrite() = 0;
 #endif
@@ -145,6 +154,7 @@ namespace mongo {
             void droppingDb(string db) { }
             bool awaitCommit() { return false; }
             bool commitNow() { return false; }
+            void commitIfNeeded() { }
 #if defined(_DEBUG)
             void debugCheckLastDeclaredWrite() {}
 #endif
@@ -159,6 +169,7 @@ namespace mongo {
             void droppingDb(string db);
             bool awaitCommit();
             bool commitNow();
+            void commitIfNeeded();
 #if defined(_DEBUG)
             void debugCheckLastDeclaredWrite();
 #endif