The INNODB_CACHED_INDEXES table reports the number of index pages cached in the InnoDB buffer pool for each index.

Examples:

This query returns the number of index pages cached in the InnoDB buffer pool for a specific index:

mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_CACHED_INDEXES WHERE INDEX_ID=65\G
*************************** 1. row ***************************
      INDEX_ID: 65
N_CACHED_PAGES: 45
1 row in set (0.00 sec)

This query returns the number of index pages cached in the InnoDB buffer pool for each index, and uses the INNODB_SYS_INDEXES and INNODB_SYS_TABLES to resolve the table name and index name for each INDEX_ID value.

SELECT
  tables.name AS table_name,
  indexes.name AS index_name,
  cached.n_cached_pages AS n_cached_pages
FROM
  INFORMATION_SCHEMA.INNODB_CACHED_INDEXES AS cached,
  INFORMATION_SCHEMA.INNODB_SYS_INDEXES AS indexes,
  INFORMATION_SCHEMA.INNODB_SYS_TABLES AS tables
WHERE
  cached.index_id = indexes.index_id
  AND indexes.table_id = tables.table_id;

Notes: