clear_query_cache

# File activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb, line 177
        def clear_query_cache
          if @pinned_connection
            # With transactional fixtures, and especially systems test
            # another thread may use the same connection, but with a different
            # query cache. So we must clear them all.
            @query_cache_version.increment
          end
          query_cache.clear
        end