Create search_index_0 to search_index_15 tables and shard each index by
account id. MySQL has no ability to pre-filter fulltext indexes by
another field so this is the best bet for improving performance.
Each fulltest index internally creates 11 sub tables (see
https://dev.mysql.com/doc/refman/8.4/en/innodb-fulltext-index.html) so
actually we have 192 tables in total here.
The search_index table name is generated dynamically based on the
account_id.
Mike Dalessio