slow queries

Hi, I am getting this error all the time in the query montior

Query:
SELECT DISTINCT YEAR( post_date ) AS year, MONTH( post_date ) AS month
FROM wp_posts
WHERE post_type = ‘attachment’
ORDER BY post_date DESC

Caller:
W3TC\DbCache_WpdbNew->default_query

I am on a dedicated server with over 16 cores and 64gb of ram, I am using Disk Echance as page cache

No minify

Database cache: Memcached
Object Cache: redis
and a reverse proxy (varnish)

Any help on this error?

The page I need help with: [log in to see the link]