TiDB using TiUP doesn't return an error for max allow packet overflow

[espresso98]

Bug Report

1. Minimal reproduce step

DROP TABLE IF EXISTS t3;
set @max_allowed_packet=@@global.max_allowed_packet;
set @net_buffer_length=@@global.net_buffer_length;
CREATE TABLE t3 (c31 INT NOT NULL, c32 LONGTEXT,
                 PRIMARY KEY (c31)) charset latin1;
INSERT INTO t3 VALUES(100,'a');
INSERT INTO t3 VALUES(111,'abcd');
INSERT INTO t3 VALUES(122,'b');
UPDATE t3 SET c32= CONCAT(c32, REPEAT('a', @max_allowed_packet-1)); 
SELECT c31, LENGTH(c32) FROM t3;
DROP TABLE t3;

2. What did you expect to see?

mysql> UPDATE t3 SET c32= CONCAT(c32, REPEAT('a', @max_allowed_packet-1)); 
SELECT c31, LENGTH(c32) FROM t3;
DROP TABLE t3;
ERROR 1301 (HY000): Result of concat() was larger than max_allowed_packet (67108864) - truncated
mysql> SELECT c31, LENGTH(c32) FROM t3;
+-----+-------------+
| c31 | LENGTH(c32) |
+-----+-------------+
| 100 |           1 |
| 111 |           4 |
| 122 |           1 |
+-----+-------------+
3 rows in set (0.00 sec)

3. What did you see instead

tidb> UPDATE t3 SET c32= CONCAT(c32, REPEAT('a', @max_allowed_packet-1)); 
Query OK, 3 rows affected (0.00 sec)
Rows matched: 3  Changed: 3  Warnings: 0

tidb> SELECT c31, LENGTH(c32) FROM t3;
+-----+-------------+
| c31 | LENGTH(c32) |
+-----+-------------+
| 100 |        NULL |
| 111 |        NULL |
| 122 |        NULL |
+-----+-------------+
3 rows in set (0.00 sec)

4. What is your TiDB version?

tidb_version(): Release Version: v6.0.0
Edition: Community
Git Commit Hash: 36a9810441ca0e496cbd22064af274b3be771081
Git Branch: heads/refs/tags/v6.0.0
UTC Build Time: 2022-03-31 10:27:58
GoVersion: go1.18
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)

[zanmato1984]

I ran the case in my local, in one mysql client (interactive mode, so all the statements are in the same session. The result is as expected.

Were you running those statements in separate sessions? (So that set @max_allowed_packet=@@global.max_allowed_packet; won't affect the subsequent statements.)

@espresso98

[zanmato1984]

I'm lowering the severity to minor before further information is supplied.

[morgo]

I believe this was fixed in #33651

Note that to get this test case to work correctly, you will need to modify your tidb.toml configuration file to change the txn-entry-size-limit to greater than 64M (the default for max-allowed-packet).

It is scheduled to be cherry picked to 6.0, but has not happened yet.. but because it's fixed in master I believe we can close this issue.

[zanmato1984]

Thank you @morgo . Closing.