Performance Codeigniter, + 2 million records.

Good morning people!

I have a problem with Code requests, when it has less than 1 million records, it loads considerably fast, starting from that mark it takes a long time to request.

A very important detail is that, even with this large number of records in the database table, it does not consume more than 1% of CPU and memory processing.

There is no limitation by the server, we test a benchmark and it consumes server resources normally.

Have you ever gone through this type of problem?