Make MariaDB use more memory
Make MariaDB use more memory

* Reduce max connections from 150 to 50, the top ever was 4.
* Increase innodb_buffer_pool_size to 500MB, to give some comfort for
  growth: the DB is currently about 60 MB but should grow a lot.
* Loosen up the query_cache limits, currently it's used too little.

MariaDB [(none)]> SHOW STATUS LIKE "qcache%";
+-------------------------+----------+
| Variable_name           | Value    |
+-------------------------+----------+
| Qcache_free_blocks      | 2548     |
| Qcache_free_memory      | 14334168 |
| Qcache_hits             | 143634   |
| Qcache_inserts          | 658558   |
| Qcache_lowmem_prunes    | 265158   |
| Qcache_not_cached       | 202239   |
| Qcache_queries_in_cache | 2161     |
| Qcache_total_blocks     | 6928     |
+-------------------------+----------+
8 rows in set (0.00 sec)

Bug: https://phabricator.wikimedia.org/T86473

Nikerabbit/intense-salt