fix(txn): remove redundant keys/preds while merging txn context (#142)

TxnContext.Keys is used as a map. This PR removes the redundant keys while merging the transaction context.

acl_test.go

@@ -29,14 +29,13 @@ import (
 )
 
 var (
-	grootpassword = "password"
-	username      = "alice"
-	userpassword  = "alicepassword"
-	readpred      = "predicate_to_read"
-	writepred     = "predicate_to_write"
-	modifypred    = "predicate_to_modify"
-	unusedgroup   = "unused"
-	devgroup      = "dev"
+	username     = "alice"
+	userpassword = "alicepassword"
+	readpred     = "predicate_to_read"
+	writepred    = "predicate_to_write"
+	modifypred   = "predicate_to_modify"
+	unusedgroup  = "unused"
+	devgroup     = "dev"
 
 	dgraphAddress = "127.0.0.1:9180"
 	adminUrl      = "http://127.0.0.1:8180/admin"

txn.go

@@ -48,6 +48,9 @@ var (
 type Txn struct {
 	context *api.TxnContext
 
+	keys  map[string]struct{}
+	preds map[string]struct{}
+
 	finished   bool
 	mutated    bool
 	readOnly   bool
@@ -63,6 +66,8 @@ func (d *Dgraph) NewTxn() *Txn {
 		dg:      d,
 		dc:      d.anyClient(),
 		context: &api.TxnContext{},
+		keys:    make(map[string]struct{}),
+		preds:   make(map[string]struct{}),
 	}
 }
 
@@ -266,8 +271,13 @@ func (txn *Txn) mergeContext(src *api.TxnContext) error {
 	if txn.context.StartTs != src.StartTs {
 		return errors.New("StartTs mismatch")
 	}
-	txn.context.Keys = append(txn.context.Keys, src.Keys...)
-	txn.context.Preds = append(txn.context.Preds, src.Preds...)
+
+	for _, key := range src.Keys {
+		txn.keys[key] = struct{}{}
+	}
+	for _, pred := range src.Keys {
+		txn.preds[pred] = struct{}{}
+	}
 	return nil
 }
 
@@ -280,6 +290,16 @@ func (txn *Txn) commitOrAbort(ctx context.Context) error {
 		return nil
 	}
 
+	txn.context.Keys = make([]string, 0, len(txn.keys))
+	for key := range txn.keys {
+		txn.context.Keys = append(txn.context.Keys, key)
+	}
+
+	txn.context.Preds = make([]string, 0, len(txn.preds))
+	for pred := range txn.preds {
+		txn.context.Preds = append(txn.context.Preds, pred)
+	}
+
 	ctx = txn.dg.getContext(ctx)
 	_, err := txn.dc.CommitOrAbort(ctx, txn.context)