Filtering your results
We already know how to build queries and searches by using different criteria. We know how scoring works, which document is more important for a given query, and how input text can affect ordering. But sometimes, we want to choose only a subset of our index, and the chosen criterion should not have an influence on scoring. This is the place where filters should be used.
Frankly enough, we should use filters whenever possible. If a given part of the query does not affect scoring, it is a good candidate to turn into a filter. Score calculation complicates things, and filtering is a relatively simple operation like a simple match-don't match calculation. Due to the fact that filtering is done on all index contents, the result of filtering is independent of the found documents and relationship between them. Filters can easily be cached, further increasing the overall performance of filtered queries.
Using filters
To use a filter in any search, just add filter to the query...