Rails ActiveRecord Table Indexes - When Should They Be Used?

Question

I heard again and again that you must add indexes to any foreign key that you will be joining. I also heard that you must have indexes for the fields in which the queries will be executed. Does anyone have an exhaustive list or set of recommendations when and when not to add indexes?

There should be a table size where indexes are inefficient. Should there be a limit on the number of indexes per table, or why not add an index to each column?

Any resources you can offer will be very helpful.

Thanks in advance!

Answer 1

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Answer 2

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