TYPO3 Core

When a category listing the the Backend is made, the following SQL Statements are issued:

SELECT sys_category.uid,sys_category.title,sys_category.t3ver_id,sys_category.t3ver_state,sys_category.t3ver_wsid,sys_category.t3ver_count,sys_category.hidden,sys_category.starttime,sys_category.endtime FROM sys_category WHERE sys_category.pid<>-1 AND sys_category.deleted=0 AND sys_category.sys_language_uid IN (-1, 0) ORDER BY sys_category.sorting ASC;

(Twice per Category Tree)

plus per each category element

SELECT uid FROM sys_category WHERE FIND_IN_SET('9',parent);

Possible Solution: Add two additional indexes to sys_category