Several redundant indexes are possibly created by the default migration files generated

[virajvchavan]

I was using active-record-doctor to check for possible issues with the DB schema and noticed it showed the following notices related to acts-as-taggable-on

remove index_taggings_on_tag_id - can be replaced by taggings_idx
remove index_taggings_on_taggable_id - can be replaced by taggings_idy or taggings_taggable_context_idx
remove index_taggings_on_taggable_type - can be replaced by index_taggings_on_taggable_type_and_taggable_id
remove index_taggings_on_tagger_id - can be replaced by index_taggings_on_tagger_id_and_tagger_type

These indices were added by the migration file generated by the command rake acts_as_taggable_on_engine:install:migrations.

In general, a multi-column index on column_1, column_2, ..., column_n can replace indexes on:

- column_1
- column_1, column_2
- ...
- column_1, column_2, ..., column_(n - 1)

Or is there a practical reason to keep these indices?

[fatkodima]

These are all valid suggestions from active_record_doctor. I think, these all extra indexes appeared as an oversight over time.
It is needed to do an audit of indexes for this gem.