Bug #98740 Created_tmp_disk_tables description is wrong
Submitted: 25 Feb 2020 19:59 Modified: 21 Apr 2020 18:22
Reporter: Marcelo Altmann Email Updates:
Status: Closed Impact on me:
None 
Category:MySQL Server: Documentation Severity:S3 (Non-critical)
Version:8.0 OS:Any
Assigned to: CPU Architecture:Any

[25 Feb 2020 19:59] Marcelo Altmann 
Description:
https://dev.mysql.com/doc/refman/8.0/en/server-status-variables.html

quote:

If an internal temporary table is created initially as an in-memory table but becomes too large, MySQL automatically converts it to an on-disk table. The maximum size for in-memory temporary tables is the minimum of the tmp_table_size and max_heap_table_size values. If Created_tmp_disk_tables is large, you may want to increase the tmp_table_size or max_heap_table_size value to lessen the likelihood that internal temporary tables in memory will be converted to on-disk tables.

Since internal_tmp_mem_storage_engine is now set to TempTable by default, the above description is only relevant if the user changed it back to MEMORY. 

How to repeat:
N/A
[25 Feb 2020 20:01] Marcelo Altmann 
Correct link to quoted text:

https://dev.mysql.com/doc/refman/8.0/en/server-status-variables.html#statvar_Created_tmp_d...
[25 Feb 2020 22:11] MySQL Verification Team 
Thank you for the bug report.
[21 Apr 2020 18:22] Daniel Price 
Posted by developer:
 
The Created_tmp_disk_tables status variable description has been revised. It applies to both MEMORY and TempTable overflow scenarios. However, it does not increment when temptable_use_mmap=ON, which is a known issue:

CREATED_TMP_DISK_TABLES NOT INCREMENTING FOR TEMPTABLE STORAGE ENGINE
https://bugs.mysql.com/bug.php?id=98741

Changes will appear online soon.
https://dev.mysql.com/doc/refman/8.0/en/internal-temporary-tables.html
https://dev.mysql.com/doc/refman/8.0/en/server-status-variables.html

Thank you for the bug report.