diff --git a/fdbclient/ReadYourWrites.actor.cpp b/fdbclient/ReadYourWrites.actor.cpp
index c1188d3ced..5452215d94 100644
--- a/fdbclient/ReadYourWrites.actor.cpp
+++ b/fdbclient/ReadYourWrites.actor.cpp
@@ -1479,7 +1479,7 @@ void ReadYourWritesTransaction::atomicOp( const KeyRef& key, const ValueRef& ope
 	if(key >= getMaxWriteKey())
 		throw key_outside_legal_range();
 
-	if(!isValidMutationType(operationType) || !isAtomicOp((MutationRef::Type) operationType) || operationType == MutationRef::AppendIfFits)
+	if(!isValidMutationType(operationType) || !isAtomicOp((MutationRef::Type) operationType))
 		throw invalid_mutation_type();
 
 	if(key.size() > (key.startsWith(systemKeys.begin) ? CLIENT_KNOBS->SYSTEM_KEY_SIZE_LIMIT : CLIENT_KNOBS->KEY_SIZE_LIMIT))
@@ -1898,4 +1898,4 @@ void ReadYourWritesTransaction::debugLogRetries(Optional<Error> error) {
 			transactionDebugInfo->lastRetryLogTime = now();
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/fdbclient/vexillographer/fdb.options b/fdbclient/vexillographer/fdb.options
index 17a5af781b..f872a661e7 100644
--- a/fdbclient/vexillographer/fdb.options
+++ b/fdbclient/vexillographer/fdb.options
@@ -217,6 +217,9 @@ description is not currently required but encouraged.
     <Option name="bit_xor" code="8"
             paramType="Bytes" paramDescription="value with which to perform bitwise xor"
             description="Performs a bitwise ``xor`` operation.  If the existing value in the database is not present or shorter than ``param``, it is first extended to the length of ``param`` with zero bytes.  If ``param`` is shorter than the existing value in the database, the existing value is truncated to match the length of ``param``."/>
+    <Option name="append_if_fits" code="9"
+            paramType="Bytes" paramDescription="value to append to the database value"
+            description="Append the value provided to the end of the existing value already in the database at the given key. This will only append the value if the final value is less than or equal to the maximum value size. Warning: However, no error is surfaced back to the user because the mutation will not be applied until after the transaction has been committed. Therefore, it is only safe to use this mutation type if one can guarantee that one will keep the total value under the maximum size."/>
     <Option name="max" code="12"
             paramType="Bytes" paramDescription="value to check against database value"
             description="Performs a little-endian comparison of byte strings. If the existing value in the database is not present or shorter than ``param``, it is first extended to the length of ``param`` with zero bytes.  If ``param`` is shorter than the existing value in the database, the existing value is truncated to match the length of ``param``. The larger of the two values is then stored in the database."/>
diff --git a/fdbserver/workloads/FuzzApiCorrectness.actor.cpp b/fdbserver/workloads/FuzzApiCorrectness.actor.cpp
index ec7d345d6e..6804f94a2f 100644
--- a/fdbserver/workloads/FuzzApiCorrectness.actor.cpp
+++ b/fdbserver/workloads/FuzzApiCorrectness.actor.cpp
@@ -862,7 +862,7 @@ struct FuzzApiCorrectnessWorkload : TestWorkload {
 				std::make_pair( error_code_key_too_large, ExceptionContract::requiredIf(key.size() > (key.startsWith(systemKeys.begin) ? CLIENT_KNOBS->SYSTEM_KEY_SIZE_LIMIT : CLIENT_KNOBS->KEY_SIZE_LIMIT)) ),
 				std::make_pair( error_code_value_too_large, ExceptionContract::requiredIf(value.size() > CLIENT_KNOBS->VALUE_SIZE_LIMIT) ),
 				std::make_pair( error_code_invalid_mutation_type, ExceptionContract::requiredIf(
-							!isValidMutationType(op) || !isAtomicOp((MutationRef::Type) op) || op == MutationRef::AppendIfFits ) ),
+							!isValidMutationType(op) || !isAtomicOp((MutationRef::Type) op)) ),
 				std::make_pair( error_code_key_outside_legal_range, ExceptionContract::requiredIf(
 							(key >= (workload->useSystemKeys ? systemKeys.end : normalKeys.end))) ),
 				std::make_pair( error_code_client_invalid_operation, ExceptionContract::requiredIf(
diff --git a/fdbserver/workloads/RandomSelector.actor.cpp b/fdbserver/workloads/RandomSelector.actor.cpp
index 11dab310d9..5a7cd61d01 100644
--- a/fdbserver/workloads/RandomSelector.actor.cpp
+++ b/fdbserver/workloads/RandomSelector.actor.cpp
@@ -138,7 +138,7 @@ struct RandomSelectorWorkload : TestWorkload {
 
 			try {
 				for(i = 0; i < g_random->randomInt(self->minOperationsPerTransaction,self->maxOperationsPerTransaction+1); i++) {
-					j = g_random->randomInt(0,15);
+					j = g_random->randomInt(0,16);
 					if( j < 3 ) {
 						myKeyA = format( "%010d", g_random->randomInt( 0, self->maxKeySpace+1 ) );
 						myValue = format("%d", g_random->randomInt( 0, 10000000 ) );
@@ -237,30 +237,30 @@ struct RandomSelectorWorkload : TestWorkload {
 							}
 						}
 					}
-					//else if( j < 8 ) {
-					//	myKeyA = format( "%010d", g_random->randomInt( 0, self->maxKeySpace+1 ) );
-					//	myRandomIDKey = format( "%010d", g_random->randomInt(0, 1000000000) );
-					//	myValue = format("%d", g_random->randomInt( 0, 10000000 ) );
-					//	//TraceEvent("RYOWappendIfFits").detail("Key",myKeyA).detail("Value", myValue);
-					//	trRYOW.atomicOp(StringRef(clientID + "b/" + myKeyA), myValue, MutationRef::AppendIfFits);
-					//			
-					//	loop {
-					//		try {
-					//			tr.set(StringRef(clientID + "z/" + myRandomIDKey), StringRef());
-					//			tr.atomicOp(StringRef(clientID + "d/" + myKeyA), myValue, MutationRef::AppendIfFits);
-					//			Void _ = wait( tr.commit() );
-					//			break;
-					//		} catch (Error& e) {
-					//			error = e;
-					//			Void _ = wait( tr.onError(e) );
-					//			if(error.code() == error_code_commit_unknown_result) {
-					//				Optional<Value> thing = wait(tr.get(StringRef(clientID+"z/"+myRandomIDKey)));
-					//				if (thing.present()) break;
-					//			}
-					//		}
-					//	}
-					//}
 					else if( j < 8 ) {
+						myKeyA = format( "%010d", g_random->randomInt( 0, self->maxKeySpace+1 ) );
+						myRandomIDKey = format( "%010d", g_random->randomInt(0, 1000000000) );
+						myValue = format("%d", g_random->randomInt( 0, 10000000 ) );
+						//TraceEvent("RYOWappendIfFits").detail("Key",myKeyA).detail("Value", myValue);
+						trRYOW.atomicOp(StringRef(clientID + "b/" + myKeyA), myValue, MutationRef::AppendIfFits);
+
+						loop {
+							try {
+								tr.set(StringRef(clientID + "z/" + myRandomIDKey), StringRef());
+								tr.atomicOp(StringRef(clientID + "d/" + myKeyA), myValue, MutationRef::AppendIfFits);
+								Void _ = wait( tr.commit() );
+								break;
+							} catch (Error& e) {
+								error = e;
+								Void _ = wait( tr.onError(e) );
+								if(error.code() == error_code_commit_unknown_result) {
+									Optional<Value> thing = wait(tr.get(StringRef(clientID+"z/"+myRandomIDKey)));
+									if (thing.present()) break;
+								}
+							}
+						}
+					}
+					else if( j < 9 ) {
 						myKeyA = format( "%010d", g_random->randomInt( 0, self->maxKeySpace+1 ) );
 						myRandomIDKey = format( "%010d", g_random->randomInt(0, 1000000000) );
 						myValue = format("%d", g_random->randomInt( 0, 10000000 ) );
@@ -283,7 +283,7 @@ struct RandomSelectorWorkload : TestWorkload {
 							}
 						}
 					}
-					else if( j < 9 ) {
+					else if( j < 10 ) {
 						myKeyA = format( "%010d", g_random->randomInt( 0, self->maxKeySpace+1 ) );
 						myRandomIDKey = format( "%010d", g_random->randomInt(0, 1000000000) );
 						myValue = format("%d", g_random->randomInt( 0, 10000000 ) );
@@ -306,7 +306,7 @@ struct RandomSelectorWorkload : TestWorkload {
 							}
 						}
 					}
-					else if( j < 10 ) {
+					else if( j < 11 ) {
 						myKeyA = format( "%010d", g_random->randomInt( 0, self->maxKeySpace+1 ) );
 						myRandomIDKey = format( "%010d", g_random->randomInt(0, 1000000000) );
 						myValue = format("%d", g_random->randomInt( 0, 10000000 ) );
@@ -329,7 +329,7 @@ struct RandomSelectorWorkload : TestWorkload {
 							}
 						}
 					}
-					else if (j < 11) {
+					else if (j < 12) {
 						myKeyA = format("%010d", g_random->randomInt(0, self->maxKeySpace + 1));
 						myRandomIDKey = format("%010d", g_random->randomInt(0, 1000000000));
 						myValue = format("%d", g_random->randomInt(0, 10000000));
@@ -353,7 +353,7 @@ struct RandomSelectorWorkload : TestWorkload {
 							}
 						}
 					}
-					else if (j < 12) {
+					else if (j < 13) {
 						myKeyA = format("%010d", g_random->randomInt(0, self->maxKeySpace + 1));
 						myRandomIDKey = format("%010d", g_random->randomInt(0, 1000000000));
 						myValue = format("%d", g_random->randomInt(0, 10000000));
@@ -377,7 +377,7 @@ struct RandomSelectorWorkload : TestWorkload {
 							}
 						}
 					}
-					else if (j < 13) {
+					else if (j < 14) {
 						myKeyA = format("%010d", g_random->randomInt(0, self->maxKeySpace + 1));
 						myRandomIDKey = format("%010d", g_random->randomInt(0, 1000000000));
 						myValue = format("%d", g_random->randomInt(0, 10000000));
@@ -401,7 +401,7 @@ struct RandomSelectorWorkload : TestWorkload {
 							}
 						}
 					}
-					else if (j < 14) {
+					else if (j < 15) {
 						myKeyA = format("%010d", g_random->randomInt(0, self->maxKeySpace + 1));
 						myRandomIDKey = format("%010d", g_random->randomInt(0, 1000000000));
 						myValue = format("%d", g_random->randomInt(0, 10000000));