For InnoDB tables that have a PK index and no other indexes, the value of IS.TABLES.INDEX_LENGTH is 0. This seems OK given that InnoDB tables are index organized on the PK.

For InnoDB tables that have a PK index and a secondary index, the value of IS.TABLES.INDEX_LENGTH is greater than 0. I assume that is accurate but I am not certain.

For InnoDB tables that have a PK index and a vector index, the value of IS.TABLES.INDEX_LENGTH is still 0. I prefer that INDEX_LENGTH be non-zero to make it easier to track index sizes.

Assuming I know how to encode the name of the ibd file it uses, I can do:

MariaDB [information_schema]> select * from innodb_sys_tablespaces where name = "test/t1#i#01"\G

*************************** 1. row ***************************

         SPACE: 39

          NAME: test/t1#i#01

          FLAG: 33

    ROW_FORMAT: Dynamic

     PAGE_SIZE: 16384

      FILENAME: ./test/t1#i#01.ibd

 FS_BLOCK_SIZE: 4096

     FILE_SIZE: 142606336

ALLOCATED_SIZE: 142655488

1 row in set (0.001 sec)