QuestDB Head of DevRel here ... Yes, it can be a replacement of Postgres and it will be cheaper and faster. That being said, PGwire is still in alpha and is not 100% covered yet, so while migrating is possible, 100% Postgres Wire Protocol compatibility is not there yet.

For traditional transactional RDBMS data, I don't think it's a very common choice. For Time Series data, QuestDB is by far the fastest choice for Postgres-compatible SQL Time Series databases.

This is great if it works well. Drop-in replacement would be great for systems with DB abstraction like in django, sqlalchemy.

Yeah, I checked it out and wanted to use but a bunch of regular old SQL queries don't work. Please add support for the old fashioned group by syntax! (This will be helpful for getting to a true drop-in replacement!)

QuestDB dev here. We added support for GROUP BY syntax in yesterday's release