As this is a performance related change the main way to test is a before and after. In terms of correctness everything should still be covered by unit tests and generally be a transparent change in terms of funcationality. Note: We have not exhaustively demonstrated the performance change between each and every index addition, but for example here is the explain plan for an example using the standard log: 1) Before the patch is applied run an explain plan on the biggest database you can find with lots of logs MariaDB [a_database]> explain SELECT * FROM mdl_logstore_standard_log WHERE realuserid = 2 ORDER BY timecreated DESC, id DESC LIMIT 0 , 10000000 \G; *************************** 1 . row *************************** id: 1 select_type: SIMPLE table: mdl_logstore_standard_log type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 7035760 Extra: Using where; Using filesort 1 row in set ( 0.004 sec)   MariaDB [a_database]> SELECT * FROM mdl_logstore_standard_log WHERE realuserid = 2 ORDER BY timecreated DESC, id DESC LIMIT 0 , 10000000 \G; - snip! - 10047 rows in set ( 9.630 sec)   MariaDB [a_database]> SELECT * FROM mdl_logstore_standard_log WHERE realuserid = 2 ORDER BY timecreated DESC, id DESC LIMIT 0 , 10000000 \G; - snip! - 10047 rows in set ( 14.776 sec) 2) Apply the patch and rerun the explain plan with indexes/foreign-keys, and confirm that is it using the index and also much faster: MariaDB [a_database]> explain SELECT * FROM mdl_logstore_standard_log WHERE realuserid = 2 ORDER BY timecreated DESC, id DESC LIMIT 0 , 10000000 \G; *************************** 1 . row *************************** id: 1 select_type: SIMPLE table: mdl_logstore_standard_log type: ref possible_keys: mdl_logsstanlog_rea_ix key: mdl_logsstanlog_rea_ix key_len: 9 ref: const rows: 18610 Extra: Using where; Using filesort 1 row in set ( 0.000 sec)   MariaDB [a_database]> SELECT * FROM mdl_logstore_standard_log WHERE realuserid = 2 ORDER BY timecreated DESC, id DESC LIMIT 0 , 10000000 ; - snip! - 10047 rows in set ( 0.091 sec)   MariaDB [a_database]> SELECT * FROM mdl_logstore_standard_log WHERE realuserid = 2 ORDER BY timecreated DESC, id DESC LIMIT 0 , 10000000 ; - snip! - 10047 rows in set ( 0.103 sec)