Table converted from myISAM to INNODB is slowing down a query - mysql

Question

I have a table that was converted from myISAM to INNODB that is slowing down a query. This is a big table with lot of indexes. MyIsam (on mysql5.6) returns result instantly, INNODB (on mysql5.7) takes 2 to 3 seconds. fnota is float. serieid and epnumber are int. Any idea why this is taking more time when doing index_merge?
Explain on MYISAM TABLE:
explain SELECT count( fnota ) , avg( fnota ) FROM myrates
WHERE serieid =4376 AND epnumber ='149'\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: myrates
type: ref
possible_keys: serieid,epnumber,serieid_2
key: serieid_2
key_len: 8
ref: const,const
rows: 8207
Extra: Using index condition
Explain on INNODB Table:
explain SELECT count( fnota ) , avg( fnota ) FROM myrates
WHERE serieid =4376 AND epnumber ='149'\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: myrates
partitions: NULL
type: index_merge
possible_keys: serieid,epnumber,serieid_2
key: serieid,epnumber,serieid_2
key_len: 4,4,8
ref: NULL
rows: 2
filtered: 100.00
Extra: Using intersect(serieid,epnumber,serieid_2); Using where
Indexes:
SHOW INDEX FROM myrates;
+---------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| myrates | 0 | fbid | 1 | userid | A | 1405506 | NULL | NULL | | BTREE | | |
| myrates | 0 | fbid | 2 | serieid | A | 8617224 | NULL | NULL | | BTREE | | |
| myrates | 0 | fbid | 3 | epnumber | A | 139638192 | NULL | NULL | | BTREE | | |
| myrates | 1 | serieid | 1 | serieid | A | 257656 | NULL | NULL | | BTREE | | |
| myrates | 1 | epnumber | 1 | epnumber | A | 93431 | NULL | NULL | | BTREE | | |
| myrates | 1 | serieid_2 | 1 | serieid | A | 186213 | NULL | NULL | | BTREE | | |
| myrates | 1 | serieid_2 | 2 | epnumber | A | 3309332 | NULL | NULL | | BTREE | | |
| myrates | 1 | userid | 1 | userid | A | 866339 | NULL | NULL | | BTREE | | |
| myrates | 1 | userid | 2 | serieid | A | 4656575 | NULL | NULL | | BTREE | | |
+---------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
SHOW CREATE TABLE MYRATES;
Table: myrates
Create Table: CREATE TABLE `myrates` (
`userid` bigint(10) NOT NULL,
`serieid` int(6) NOT NULL,
`epnumber` float NOT NULL,
`nota` int(6) NOT NULL DEFAULT '0',
`fnota` float NOT NULL,
`timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
UNIQUE KEY `fbid` (`userid`,`serieid`,`epnumber`),
KEY `serieid` (`serieid`),
KEY `epnumber` (`epnumber`),
KEY `serieid_2` (`serieid`,`epnumber`),
KEY `userid` (`userid`,`serieid`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

Answer 1

DESCRIBE does not precisely spell out the indexes you have. Please provide SHOW CREATE TABLE. It sounds like it is getting confused over your long list of overlapping indexes.
When you have a composite index such as (serieid, epnumber) you don't also need (serieid). Drop the latter index to 'fix' the problem.
It seems that key "userid" is redundant also, given that "fbid" starts with both of its two columns in the same order.