Improve explanation of MariaDB (Ubuntu 18.04 is also affected)

fixes #1

README.md

@@ -22,16 +22,16 @@ And then run the `tank` binary:
 $ $GOPATH/bin/tank --config config.yaml run --listen localhost:8040
 ```
 
-### Problem with MariaDB on Debian 9 (stretch)
+### Problem with some versions of MariaDB
 
-If you start `tank` for the first time you may get the following error message:
+If you start `tank` for the first time using MariaDB you may get the following error message:
 
 ```
 running database migrations failed: Error 1071: Specified key was too long; max key length is 767 bytes
 ```
 
-This most likely means you are using a MariaDB server running on Debian 9 (stretch). Please read
-[contrib/mariadb-stretch-err1071.md](/contrib/mariadb-stretch-err1071.md) for help.
+This most likely means you are using an older version of MariaDB with the default character-set set to
+`utf8mb4`. Please read [contrib/mariadb-stretch-err1071.md](/contrib/mariadb-stretch-err1071.md) for help.
 
 If you encouter this problem on any other platform please let us know!
 

contrib/mariadb-stretch-err1071.md

@@ -2,14 +2,15 @@
 
 ## Background
 
-`tank` stores shows using it's name as primary key. Since this is a string it
-by default is mapped to a `VARCHAR(255)` inside the database.
-Starting with Debian 9 (stretch) MariaDB is installed instead of mySQL. Debian also
-switched to `utf8mb4` as the default character set in an attempt to support Emoji's
-stored as UTF-8 characters in the database.
-This means that a `VARCHAR(255)` is now 1021 bytes long which exceeds the maximum
-length (767 bytes) for primary key indices when `innodb` is used (also the default since quite
-some time).
+`tank` stores shows using it's name as primary key. Since this is a string it by default is
+mapped to a `VARCHAR(255)` at the database level.
+Some Linux distributions, i.e. Debian 9 (stretch) or Ubuntu 18.04 (bionic) have switched to
+the mySQL fork MariaDB. At least Debian und Ubuntu also switched to `utf8mb4` as
+the default character-set. This is an attempt to support Emoji's stored as UTF-8 characters in
+the database for applications like Wordpress.
+When using `utf8mb4` a `VARCHAR(255)` field can be up to 1021 bytes long. This exceeds the
+maximum length (767 bytes) for primary key indices on older version of the `innodb` file and row
+formats.
 
 ## Possible Workarounds
 
@@ -26,7 +27,7 @@ create database tank CHARACTER SET utf8 COLLATE utf8_general_ci;
 
  * Debian has [backported](https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=886756) some
    changes to the MariaDB version in Debian Stretch. Because of this it is possible to switch
-   to the new innodb layout which is the default for newer version of MariaDB as well as mySQL.
+   to the new innodb file and row format.
    You can do this by adding the following to the `[mysqld]` section of
    `/etc/mysql/mariadb.conf.d/50-server.cnf`:
    ```ini
@@ -35,14 +36,19 @@ innodb_file_per_table     = On
 innodb_large_prefix       = On
 innodb_default_row_format = dynamic
    ```
+   As far as i can see Ubuntu did not add this patch to it's packages but starting with 10.2
+   MariaDB uses the new format by default. This means you can work around the issue by using
+   the packages provided by the [MariaDB Foundation](https://downloads.mariadb.org/mariadb/repositories/).
 
  * Consider switching to another DBMS:
    * `tank` also works with postgres
    * you may use the mySQL Community Packages from [Oracle](https://dev.mysql.com/doc/refman/5.7/en/linux-installation-debian.html)
-   * [Percona Server](https://www.percona.com/software/mysql-database/percona-server) is drop-in replacement for mySQL
+   * [Percona Server](https://www.percona.com/software/mysql-database/percona-server) is a drop-in
+     replacement for mySQL
 
- * If for some reason none of the above is applicable as a last resort you can apply the patch below.
-   This limits the length for show names to 191 characters which is just short enough to not exceed the limit.
+ * If for some reason none of the above is applicable, as a last resort, you can apply the
+   patch below. This limits the length for show names to 191 characters which is just short
+   enough to not exceed the limit.
 
    ```patch
 diff --git a/store/types.go b/store/types.go