The complaint was about IndexedDB access, not local memory. Folk mentioning this are usually referring to the disastrous implementation in Chrome: see https://dev.to/skhmt/why-are-indexeddb-operations-significan... and https://jlongster.com/future-sql-web

Wow. Orders of magnitude slower than ff.

indexedDB is quite a low level in what the interface gives you.

This includes what options you have available for querying (just accessing a key range, upper/lower bound, forward or backwards (backwards can be much slower), rather than a full query language like SQL etc..

So you need to design your app / data format and pre-plan any queries so you'll have the indexes you need, or do some glue logic to combine indexes as needed.