Re: Slow query log 'Rows_examined' vs 'explain select' rows

[Rick James]

USE INDEX seems to have solved the problem. So, it was probably the statistics. I dislike "USE INDEX" because it tends to pin you in a solution that works for one case, but makes another case worse. Still, that may be the 'right' answer for your query.

One Rule of Thumb for partitioning -- Don't use it unless you have at least a million rows.
http://mysql.rjweb.org/doc.php/ricksrots#partitioning
A partitioned table will take some extra disk space, but rarely more than a few percent or maybe 100MB.
Note: one of the RoTs says not to have very many partitions.

Both of these exclude :55 (Perhaps you want <= or >=, but not both)
<'2013-01-08 23:07:55'
>'2013-01-08 21:10:55

(Opinion) The "vss_" prefix on the fields (except the id) clutters queries and makes them hard to read. When JOINing, "vss." can be the alias; "vss.vss_..." is quite redundant.