[#MDEV-28490] Strange result truncation with group_concat_max

When setting group_concat_max_len to exactly one GB (1073741824) or more and using GROUP_CONCAT() in a subquery the result gets truncated as if the actual group concat limit had been set to the given value modulo 1073741824.

How to reproduce:
(this originally occurred in combination with JSON functions, but this is the most simple case I could strip it down to while still getting the same truncated results)

USE test;

DROP TABLE IF EXISTS t1;

CREATE TABLE t1(val VARCHAR(100) PRIMARY KEY);

INSERT INTO t1 VALUES('bar');

INSERT INTO t1 VALUES('foo');

SET group_concat_max_len = 1073741823; -- 1GB minus one

SHOW VARIABLES LIKE 'group_concat_max_len';

SELECT GROUP_CONCAT(val) AS simple FROM t1;

SELECT * FROM ( SELECT GROUP_CONCAT(val) AS nested FROM t1) As tmp;

SET group_concat_max_len = 1073741824; -- exactly 1GB

SHOW VARIABLES LIKE 'group_concat_max_len';

SELECT GROUP_CONCAT(val) AS simple FROM t1;

SELECT * FROM ( SELECT GROUP_CONCAT(val) AS nested FROM t1) As tmp;

SET group_concat_max_len = 1073741825; -- 1GB plus one

SHOW VARIABLES LIKE 'group_concat_max_len';

SELECT GROUP_CONCAT(val) AS simple FROM t1;

SELECT * FROM ( SELECT GROUP_CONCAT(val) AS nested FROM t1) As tmp;

SET group_concat_max_len = 1073741826; -- 1GB plus two

SHOW VARIABLES LIKE 'group_concat_max_len';

SELECT GROUP_CONCAT(val) AS simple FROM t1;

SELECT * FROM ( SELECT GROUP_CONCAT(val) AS nested FROM t1) As tmp;

SET group_concat_max_len = 2147483649; -- 2GB plus one

SHOW VARIABLES LIKE 'group_concat_max_len';

SELECT GROUP_CONCAT(val) AS simple FROM t1;

SELECT * FROM ( SELECT GROUP_CONCAT(val) AS nested FROM t1) As tmp;

Expected result:

Variable_name	Value

group_concat_max_len	1073741823

simple

bar,foo

nested

bar,foo

Variable_name	Value

group_concat_max_len	1073741824

simple

bar,foo

nested

bar,foo

Variable_name	Value

group_concat_max_len	1073741825

simple

bar,foo

nested

bar,foo

Variable_name	Value

group_concat_max_len	1073741826

simple

bar,foo

nested

bar,foo

group_concat_max_len	2147483649

simple

bar,foo

nested

bar,foo

Actual result:

Variable_name	Value

group_concat_max_len	1073741823

simple

bar,foo

nested

bar,foo

Variable_name	Value

group_concat_max_len	1073741824

simple

bar,foo

nested

Variable_name	Value

group_concat_max_len	1073741825

simple

bar,foo

nested

Variable_name	Value

group_concat_max_len	1073741826

simple

bar,foo

nested

ba

group_concat_max_len	2147483649

simple

bar,foo

nested

[MDEV-28490] Strange result truncation with group_concat_max_len=1GB Created: 2022-05-06 Updated: 2022-08-18 Resolved: 2022-05-16
Status:	Closed
Project:	MariaDB Server
Component/s:	Configuration
Affects Version/s:	10.5.15, 10.6.7, 10.7.3, 10.8.2
Fix Version/s:	10.5.16, 10.6.8, 10.7.4, 10.8.3

[MDEV-28490] Strange result truncation with group_concat_max_len=1GB Created: 2022-05-06 Updated: 2022-08-18 Resolved: 2022-05-16