Your favourite monitoring software throws an alert or sends an email after it finds the following in the mysql error log:

InnoDB: page [page id: space=8858, page number=206777] (95 records, index id 29361)

How do you find which index is corrupted from this line?

Example using the above index id listed in the error log message:

 select * from information_schema.INNODB_SYS_INDEXES where index_id = 29361;

+----------+--------------------------------+----------+------+----------+---------+-------+-----------------+
| INDEX_ID | NAME                           | TABLE_ID | TYPE | N_FIELDS | PAGE_NO | SPACE | MERGE_THRESHOLD |
+----------+--------------------------------+----------+------+----------+---------+-------+-----------------+
|    29361 | blah_longwinded_name_for_index |    11238 |    0 |        3 |       4 |  8858 |              50 |
+----------+--------------------------------+----------+------+----------+---------+-------+-----------------+
1 row in set (0.009 sec)

How do you find which table is corrupted?

Example using the above table_id listed in the output from the above SQL statement.

select * from information_schema.INNODB_SYS_TABLES where table_id = 11238;

+----------+-----------------------------------------------------+------+--------+-------+------------+---------------+------------+
| TABLE_ID | NAME                                                | FLAG | N_COLS | SPACE | ROW_FORMAT | ZIP_PAGE_SIZE | SPACE_TYPE |
+----------+-----------------------------------------------------+------+--------+-------+------------+---------------+------------+
|    11238 | database0001_production/blah_longwinded_name_table  |   41 |      8 |  8858 | Compressed |          8192 | Single     |
+----------+-----------------------------------------------------+------+--------+-------+------------+---------------+------------+

What about just as one statement…

select t.name as table_name,i.name as index_name,t.table_id,i.index_id 
from information_schema.INNODB_SYS_TABLES t
JOIN information_schema.INNODB_SYS_INDEXES i on t.table_id=i.table_id
where index_id = 29361;

+-----------------------------------------------------+--------------------------------+----------+----------+
| table_name                                          | index_name                     | table_id | index_id |
+-----------------------------------------------------+--------------------------------+----------+----------+
| database0001_production/blah_longwinded_name_table  | blah_longwinded_name_for_index | 11238    | 29361    |
+-----------------------------------------------------+--------------------------------+----------+----------+

How do I fix this corrupted index?

Use a null alter to rebuild the table.

WARNING:

1. Check the size first.
2. use a tool like pt-online-schema-change if the table is large or accessed heavily, or you are running on Galera, Percona Cluster or equivalent.
3. Did you get permission to run this on production?

eg:

ALTER TABLE <tablename> ENGINE=INNODB ;