perf: avoid to string conversion in statement parser (#453)

Author: egonelbre

aborted_transactions_test.go

@@ -919,7 +919,7 @@ func TestBatchUpdateAbortedWithError(t *testing.T) {
 		t.Fatalf("error code mismatch\nGot: %v\nWant: %v", spanner.ErrCode(err), codes.NotFound)
 	}
 
-	// Abort the transaction. The internal retry should succeed as teh same error
+	// Abort the transaction. The internal retry should succeed as the same error
 	// and the same row count is returned during the retry.
 	server.TestSpanner.PutExecutionTime(testutil.MethodCommitTransaction, testutil.SimulatedExecutionTime{
 		Errors: []error{status.Error(codes.Aborted, "Aborted")},

statement_parser.go

@@ -712,14 +712,14 @@ func (p *statementParser) calculateFindParamsResult(sql string) (string, []strin
 	for parser.pos < len(parser.sql) {
 		startPos := parser.pos
 		parser.skipWhitespacesAndComments()
-		parsedSQL.WriteString(string(parser.sql[startPos:parser.pos]))
+		parsedSQL.Write(parser.sql[startPos:parser.pos])
 		if parser.pos >= len(parser.sql) {
 			break
 		}
 		if parser.isMultibyte() {
 			startPos = parser.pos
 			parser.nextChar()
-			parsedSQL.WriteString(string(parser.sql[startPos:parser.pos]))
+			parsedSQL.Write(parser.sql[startPos:parser.pos])
 			continue
 		}
 		c := parser.sql[parser.pos]
@@ -772,7 +772,7 @@ func (p *statementParser) calculateFindParamsResult(sql string) (string, []strin
 			if err != nil {
 				return sql, nil, err
 			}
-			parsedSQL.WriteString(string(parser.sql[startPos:newPos]))
+			parsedSQL.Write(parser.sql[startPos:newPos])
 			parser.pos = newPos
 		}
 	}