We have a PHP app running against MySQL 5.7 with innoDB. The app used to be really slow. MySQL takes 100% of the CPU for a really long time, for some queries. I tried running optimize table, which innoDB just interprets as re-create table. This made matters only worse.
I enabled slow query logging as:
slow_query_log = ON
long_query_time = 5
log_queries_not_using_indexes = ON
slow_query_log_file = /var/log/mysql/mysql-slow.log
I only see the below in the log, repeated many times:
SET timestamp=1516955047;
SELECT * FROM `notification` WHERE `user_id`=4 ORDER BY `created_at` DESC LIMIT 5;
# Time: 2018-01-26T08:24:07.652626Z
# User@Host: root[root] @ localhost [] Id: 153
# Query_time: 0.000221 Lock_time: 0.000107 Rows_sent: 1 Rows_examined: 3
SET timestamp=1516955047;
SELECT
kcu.constraint_name,
kcu.column_name,
kcu.referenced_table_name,
kcu.referenced_column_name
FROM information_schema.referential_constraints AS rc
JOIN information_schema.key_column_usage AS kcu ON
(
kcu.constraint_catalog = rc.constraint_catalog OR
(kcu.constraint_catalog IS NULL AND rc.constraint_catalog IS NULL)
) AND
kcu.constraint_schema = rc.constraint_schema AND
kcu.constraint_name = rc.constraint_name
WHERE rc.constraint_schema = database() AND kcu.table_schema = database()
AND rc.table_name = 'notification' AND kcu.table_name = 'notification';
# Time: 2018-01-26T08:24:07.653082Z
# User@Host: root[root] @ localhost [] Id: 153
# Query_time: 0.000155 Lock_time: 0.000040 Rows_sent: 1 Rows_examined: 143
I want something to go on, to be able whether performance could be improved with database tuning. How do I see a list of missing indices or something like that?