mariadb: Tweak default configuration

Remove from default configuration options that are compiled in like
default paths and character set. On the other hand add few examples of
tweak options that might be handy.

Signed-off-by: Michal Hrusecky <michal.hrusecky@turris.com>

utils/mariadb/conf/50-server.cnf

@@ -14,18 +14,11 @@
 #
 # * Basic Settings
 #
-user		= mariadb
-pid-file	= /var/run/mysqld/mysqld.pid
-socket		= /var/run/mysqld/mysqld.sock
 port		= 3306
-basedir		= /usr
 # Don't put this on flash memory
-# Figure out where you are going to put the databases and run
-# mysql_install_db --force
-datadir		= /mnt/data/mysql
-# tmpdir should also not go on flash memory
-tmpdir		= /tmp
-lc-messages-dir	= /usr/share/mariadb
+# datadir		= /srv/mysql
+# tmpdir should also not go on flash memory, but needs to exist and have correct rights
+# tmpdir		= /tmp
 
 skip-external-locking
 
@@ -51,6 +44,7 @@ myisam_recover_options	= BACKUP
 # * Query Cache Configuration
 #
 query_cache_limit	= 1M
+query_cache_min_res_unit = 1k
 query_cache_size	= 16M
 
 #
@@ -88,6 +82,19 @@ max_binlog_size		= 100M
 #
 # InnoDB is enabled by default with a 10MB datafile in /var/lib/mysql/.
 # Read the manual for more InnoDB related options. There are many!
+innodb_file_per_table=1
+innodb_buffer_pool_size=64M
+innodb_flush_log_at_trx_commit=2
+innodb_log_buffer_size=32M
+innodb_max_dirty_pages_pct=90
+# You can set .._buffer_pool_size up to 50 - 80 %
+# of RAM but beware of setting memory usage too high
+#innodb_buffer_pool_size = 16M
+# Set .._log_file_size to 25 % of buffer pool size
+#innodb_log_file_size = 5M
+#innodb_log_buffer_size = 8M
+#innodb_flush_log_at_trx_commit = 1
+#innodb_lock_wait_timeout = 50
 
 #
 # * Security Features
@@ -105,25 +112,6 @@ max_binlog_size		= 100M
 # ..when MariaDB is compiled with OpenSSL:
 # ssl-cipher=TLSv1.2
 
-#
-# * Character sets
-#
-# MySQL/MariaDB default is Latin1, but in OpenWrt we rather default to the full
-# utf8 4-byte character set. See also client.cnf
-#
-# Note: In OpenWrt until mariadb 10.2.19-2 the baked-in defaults were
-# "DEFAULT_CHARSET=utf8" and "DEFAULT_COLLATION=utf8_general_ci". As MariaDB's
-# utf8 (supports three bytes per character) is not really UTF-8 (which needs up
-# to four bytes per character) this was changed. Now the baked in-defaults are
-# the upstream defaults (Latin1), but in the default configuration (like in the
-# file you are currently reading) utf8mb4 is set, which is real UTF-8.
-#
-# Of course you are free to change this, either here or in a configuration file
-# of your own which is read after this .cnf file, see my.cnf in parent folder
-# (files are read in alphabetical order).
-character-set-server  = utf8mb4
-collation-server      = utf8mb4_general_ci
-
 #
 # * Unix socket authentication plugin is built-in
 #