From 0c1d8e04089de11c3829312864c2e9313dc37ba1 Mon Sep 17 00:00:00 2001
From: Naman Jain <naman@dgraph.io>
Date: Thu, 4 Mar 2021 16:24:09 +0530
Subject: [PATCH] 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 | 15 +++++++--------
 txn.go      | 24 ++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/acl_test.go b/acl_test.go
index 37f4afd..73f6742 100644
--- a/acl_test.go
+++ b/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"
diff --git a/txn.go b/txn.go
index 82655b5..84c997c 100644
--- a/txn.go
+++ b/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)