No way to limit temporary table size when maria tables are in use

[Sergey Petrunia]

I've hit this while merging this testcase from mysql-5.1/mysql-test/insert_select.test:

CREATE TABLE t1(a INT);
# To force MyISAM temp. table in the following INSERT ... SELECT.
SET max_heap_table_size = 16384;
# To overflow the temp. table.
SET @old_myisam_data_pointer_size = @@myisam_data_pointer_size;
SET GLOBAL myisam_data_pointer_size = 2;

INSERT INTO t1 VALUES (1), (2), (3), (4), (5);

--error ER_RECORD_FILE_FULL,ER_RECORD_FILE_FULL
INSERT IGNORE INTO t1 SELECT t1.a FROM t1,t1 t2,t1 t3,t1 t4,t1 t5,t1 t6,t1 t7;

The problems are that
- Maria engine doesn't have an analog of myisam_data_pointer_size, consequently the insert will not fail and we can't run the testcase.
- Albeit there is a #define USE_MARIA_FOR_TMP_TABLES, once you have a binary there is no straightforward way to tell from SQL whether it will use maria or myisam for temporary tables.

[Sergey Petrunia (sergefp)]

Will add a server variable.

[Sergey Petrunia (sergefp)]

I think 5.1 tag should be removed and priority reduced.

Other than the mentioned testcase (which we can live without), I have never saw anything or anybody to use @@myisam_data_pointer_size value to limit temporary table size. If there is a real need to set such limit, we should add a separate variable, e.g. @@disk_temp_table_size.

With regards to inability to check the USE_MARIA_FOR_TMP_TABLES setting from SQL, that doesn't seem to be high priority (haven't seen anybody to build MariaDB with MyISAM temp.tables for a while, there are no known issues with MyISAM vs Maria temp.tables, etc.)

[Sergey Petrunia (sergefp)]

Changed tags and priority accordingly.