Logstash ability to check field value against file contents

Does anyone know of a plugin that would allow checking a field's value against the contents of a file? I'm looking to do a simple boolean check and if true have the capability to add a tag or field.

This would allow tagging of events to aid in filtering in or out on events. For example, assume you have a DNS log that has google.com in it. It would be helpful to check google.com against the Alexa top 1 million and if found tag the log with alexa. This would allow easy filtering of logs of interest by filtering out anything tagged with alexa.

I know you can do this with the ruby plugin but the performance is terrible as it would reload the file every time ruby is invoked. If there is a plugin that when loaded buffers the file contents in memory this would be incredibly fast and used for similar concepts.

Anyone know of an existing way to do this?

Sounds like the translate filter would be of use to you.