Fix for OLIO-153. Adding indexes for improving AddEvent performance
user
```ruby
#
# Licensed to the Apache Software Foundation (ASF) under one
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# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
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# 
class MoreIndexes < ActiveRecord::Migration
  def self.up
    add_index :taggings, :tag_id
    add_index :taggings, :taggable_id
    add_index :taggings, :taggable_type
  end

  def self.down
    remove_index :taggings, :tag_id
    remove_index :taggings, :taggable_id
    remove_index :taggings, :taggable_type
  end
end
```
assistant