From fbfafb3edfc378681c2bad91b1a126e7e6df3f5b Mon Sep 17 00:00:00 2001
From: Petr Evdokimov <iclaus21@gmail.com>
Date: Mon, 21 Nov 2022 13:50:08 +0300
Subject: [PATCH] Optimize 'beginSQL' runtime and memory allocations

---
 tx.go | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/tx.go b/tx.go
index 28a9af13..840ba045 100644
--- a/tx.go
+++ b/tx.go
@@ -1,7 +1,6 @@
 package pgx
 
 import (
-	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -52,19 +51,23 @@ func (txOptions TxOptions) beginSQL() string {
 	if txOptions == emptyTxOptions {
 		return "begin"
 	}
-	buf := &bytes.Buffer{}
-	buf.WriteString("begin")
+
+	buf := make([]byte, 0, 64) // 64 - maximum length of string with available options
+	buf = append(buf, "begin"...)
 	if txOptions.IsoLevel != "" {
-		fmt.Fprintf(buf, " isolation level %s", txOptions.IsoLevel)
+		buf = append(buf, " isolation level "...)
+		buf = append(buf, txOptions.IsoLevel...)
 	}
 	if txOptions.AccessMode != "" {
-		fmt.Fprintf(buf, " %s", txOptions.AccessMode)
+		buf = append(buf, ' ')
+		buf = append(buf, txOptions.AccessMode...)
 	}
 	if txOptions.DeferrableMode != "" {
-		fmt.Fprintf(buf, " %s", txOptions.DeferrableMode)
+		buf = append(buf, ' ')
+		buf = append(buf, txOptions.DeferrableMode...)
 	}
 
-	return buf.String()
+	return string(buf)
 }
 
 var ErrTxClosed = errors.New("tx is closed")