Actual if there are a lot of records of a specific entity type in database. In this case it's reasonable to disable displaying count on the list view of that entity type, since COUNT is a very slow operation in MySQL.
To disable: Administration > Entity Manager > edit specific entity type > check Disable record count.
By default EspoCRM has some pre-defined indexes. As your database gets bigger it's reasonable to create new indexes. What exactly indexes are needed depends on how you use CRM and how you customized it: what custom fields are created, default record orders are set, reports are often run, searches are usually performed, etc.
See article about how to create indexes.
It's recommended to set a value that is about 70% of your RAM.
You can consider increasing this param to speed up ORDER BY or GROUP BY. See more.
Should be large enough. See more.
We recommend to set it to