Question

What are secondary indexes?

Answer 1

Secondary indexes are indexes built over column values. In other words, let’s say you have a user table, which contains a user’s email. The primary index would be the user ID, so if you wanted to access a particular user’s email, you could look them up by their ID. However, to solve the inverse query given an email, fetch the user ID requires a secondary index.

Answer 2

Try not using secondary indexes on columns contain a high count of unique values and that will produce few results.