Add option for server-side linearizability

Author: gpahal

pydgraph/proto/api.proto

@@ -96,7 +96,13 @@ message Version {
 }
 
 message LinRead {
+	enum Sequencing {
+		CLIENT_SIDE = 0;
+		SERVER_SIDE = 1;
+	}
+
 	map<uint32, uint64> ids = 1;
+	Sequencing sequencing = 2;
 }
 
 message Latency {

pydgraph/proto/api_pb2.py

@@ -1,7 +1,7 @@
 # Generated by the gRPC Python protocol compiler plugin. DO NOT EDIT!
 import grpc
 
-import api_pb2 as api__pb2
+from . import api_pb2 as api__pb2
 
 
 class DgraphStub(object):

pydgraph/proto/api_pb2_grpc.py

@@ -47,6 +47,10 @@ def __init__(self, client):
 
         self._finished = False
         self._mutated = False
+        self._sequencing = api.LinRead.CLIENT_SIDE
+
+    def sequencing(self, sequencing):
+        self._sequencing = sequencing
 
     def query(self, q, variables=None, timeout=None, metadata=None, credentials=None):
         req = self._common_query(q, variables=variables)
@@ -57,8 +61,10 @@ def query(self, q, variables=None, timeout=None, metadata=None, credentials=None
     def _common_query(self, q, variables=None):
         if self._finished:
             raise Exception('Transaction has already been committed or discarded')
-        
-        req = api.Request(query=q, start_ts=self._ctx.start_ts, lin_read=self._ctx.lin_read)
+
+        lin_read = self._ctx.lin_read
+        lin_read.sequencing = self._sequencing
+        req = api.Request(query=q, start_ts=self._ctx.start_ts, lin_read=lin_read)
         if variables is not None:
             for key, value in variables.items():
                 if util.is_string(key) and util.is_string(value):

pydgraph/txn.py

@@ -328,8 +328,8 @@ def test_mutate_conflict(self):
 
         txn2.commit()
 
-        _ = txn.mutate(set_obj={'uid': uid, 'name': 'Manish2'})
-        self.assertRaises(pydgraph.AbortedError, txn.commit)
+        with self.assertRaises(pydgraph.AbortedError):
+            _ = txn.mutate(set_obj={'uid': uid, 'name': 'Manish2'})
 
     def test_conflict_ignore(self):
         """Tests a mutation with ignore index conflict."""