improve MySQL text searches
query_cache_size: 512000000 plus query_cache_type: 1 is really bad for performance.

If the QC is on, then every modification to a table will cause a purge of all rows for that table in the QC.  The bigger the QC is, the longer it takes.  I recommend only 50M for the size.  Or turn the QC off.  All

"the" is a poor test case since it is (assuming English) so very common. Pick some word that occurs only a few times.  Or, maybe a word that occurs once, a word that occurs about 10 times, and a word that occurs 100 times.

max_heap_table_size: 512000000 and tmp_table_size: 512000000 are also bad because they are 12% of RAM; lower to 1% of RAM.  In complex queries, those limits come into play.  If there are several complex queries running at once, you could blow out RAM.  Swapping is really bad for performance.

If you can't permanently change those settings, complain to the provider.  If they won't listen, then change providers.  That's how bad I think the settings are.  No change to "memory, cpus, disk: ssd" can fix the query_cache_size problem.