CHARACTER SETS
--------------

Starting with RT 5.0.0, the minimum supported MariaDB version is 10.2.5
because this is the first version to provide full support for 4 byte
utf8 characters in tables and indexes. Read on for details on this
change.

RT 5.0.0 now defaults MariaDB tables to utf8mb4, which is available in
versions before 10.2.5. However, before MariaDB version 10.2.5, utf8mb4
tables could not have indexes with type VARCHAR(255): the default size
for index entries was 767 bytes, which is enough for 255 chars stored
as at most 3 chars (the utf8 format), but not as 4 bytes (utf8mb4).
10.2.5 sets the default index size to 3072 for InnoDB tables, resolving
that issue.

https://mariadb.com/kb/en/changes-improvements-in-mariadb-102/
https://mariadb.com/kb/en/mariadb-1025-changelog/ (search for utf8)

In MariaDB, RT uses the utf8mb4 character set to support all
unicode characters, including the ones that are encoded with 4 bytes in
utf8 (some Kanji characters and a good number of emojis). The DB tables
and RT are both set to this character set.

If your MariaDB database is used only for RT, you can consider
setting the default character set to utf8mb4. This will
ensure that backups and other database access outside of RT have the
correct character set.

This is done by adding the following lines to the MariaDB configuration:

[mysqld]
character-set-server = utf8mb4

[client]
default-character-set = utf8mb4

You can check the values your server is using by running this command:
    mysqladmin variables | grep -i character_set

Setting the default is particularly important for mysqldump, to avoid
backups to be silently corrupted.

If the MySQL DB is shared with other applications and the default
character set cannot be set to utf8mb4, the command to backup the
database must set it explicitly:

    ( mysqldump --default-character-set=utf8mb4 rt5 --tables sessions --no-data --single-transaction; \
      mysqldump --default-character-set=utf8mb4 rt5 --ignore-table rt5.sessions --single-transaction ) \
        | gzip > rt-`date +%Y%m%d`.sql.gz

Restoring a backup is done the usual way, since the character set for
all tables is set to utf8mb4, there is no further need to tell MariaDB
about it:

    gunzip -c rt-20191125.sql.gz | mysql -uroot -p rt5

These character set updates now allow RT on MariaDB to accept and store 4-byte
characters like emojis. However, searches can still be inconsistent. You may be
able to get different or better results by experimenting with different collation
settings. For more information:

https://stackoverflow.com/a/41148052
https://mariadb.com/kb/en/character-sets/

TIME ZONE TABLES
----------------

Charts in RT can use time zone conversion for dates and this requires that
time zones are loaded into the database. MariaDB on some platforms such as
Centos (and possibly others) have time zone tables, but they are not
populated and need to be loaded manually.

On Unix-like systems, you can use the mysql_tzinfo_to_sql utility, which
uses the zoneinfo data provided on the system. Documentation on loading the
time zones using the mysql_tzinfo_to_sql tool can be found at:

https://mariadb.com/kb/en/mysql_tzinfo_to_sql/

You can confirm that timezone tables are populated by running:

    select CONVERT_TZ( '2020-07-27 20:00:00', 'UTC', 'Europe/London' );

If the result is "2020-07-27 21:00:00" the timezones are populated. If the
result is NULL then time zones are not populated.
