I have multiple drupal 7 sites running on my shared hosting. Suddenly almost all of my drupal sites began running very slow. After some searching I found that I had 132k slow queries of the 140M queries executes.
So I turned on de debug query option in the Devel module and got this:
Executed 230 queries in 18868.24 ms. Queries exceeding 5 ms are highlighted. Page execution time was 21632.34 ms. Memory used at: devel_boot()=2.61 MB, devel_shutdown()=47.54 MB, PHP peak=48 MB.
After looking at the SELECT-query list I noticed that there are a lot of cache-queries that run slowly:
SELECT cid, data, created, expire, serialized FROM cache_views WHERE cid IN (:cids_0)
Not only for 'cache_views' but also other cache-tables:
In PHPMYADMIN I also notice that a lot of queries have been removed from the cache:
Qcache_lowmem_prunes: 35.2M (of 143M queries)
I already checked if there were modules enabled in the DB but deleted on the drupal site.
I hope this is enough info to get some help.