added workarounds for sql error 1071

README.md

@@ -13,7 +13,7 @@ $ go get gitlab.servus.at/autoradio/tank/...
 Create configuration file see:
   https://gitlab.servus.at/autoradio/tank/blob/master/contrib/sample-cfg.yaml
 
-Make sure that the directory pointed to by ```store.path``` exists and is writeable
+Make sure that the directory pointed to by `store.path` exists and is writeable
 for the user running the daemon
 
 And then run the `tank` binary:
@@ -24,7 +24,7 @@ $ $GOPATH/bin/tank --config config.yaml run --listen localhost:8000
 
 ### Problem with MariaDB on Debian 9 (stretch)
 
-If you start ```tank``` for the first time you may get the following error message:
+If you start `tank` for the first time you may get the following error message:
 
 ```
 running database migrations failed: Error 1071: Specified key was too long; max key length is 767 bytes
@@ -52,8 +52,8 @@ You may run the daemon using the following command:
 $ ./contrib/run.sh
 ```
 
-This is using ```contrib/sample-cfg.yaml``` and depends on a mysql or postgres server
-running on localhost. You may use the scripts inside ```contrib/``` to start docker
+This is using `contrib/sample-cfg.yaml` and depends on a mysql or postgres server
+running on localhost. You may use the scripts inside `contrib/` to start docker
 containers for this purpose.
 
 ### mysql
@@ -102,5 +102,5 @@ After the daemon has ran the initial migrations you may check out the schema of
 $$$ psql < info.sql
 ```
 
-Once you are done with the database you can stop the server by pressing ```CTRL-C``` inside the
+Once you are done with the database you can stop the server by pressing `CTRL-C` inside the
 terminal of the server.

contrib/mysql/init.sql

 drop database tank;
 create database tank;
+-- create database tank CHARACTER SET utf8 COLLATE utf8_general_ci;
 grant all privileges on tank.* to 'tank'@'%' identified by 'aura';
 use tank;

mariadb-stretch-err1071.md

 # MariaDB `Error 1071: Specified key was too long`
 
-tba...
+## Background
+
+`tank` stores groups 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).
+
+## Possible Workarounds
+
+There are several possible workarounds for the problem:
+
+ * create the database using `utf8` (not `utf8mb4`):
+   When creating the database use the following command:
+   ```mysql
+create database tank CHARACTER SET utf8 COLLATE utf8_general_ci;
+   ```
+   This means you won't be able to use Emoji's in File Metadata.
+
+ * 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.
+   You can do this by adding the following to the `[mysqld]` section of
+   `/etc/mysql/mariadb.conf.d/50-server.cnf`:
+   ```ini
+innodb_file_format        = Barracuda
+innodb_file_per_table     = On
+innodb_large_prefix       = On
+innodb_default_row_format = dynamic
+   ```
+
+ * 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
+
+ * 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 group 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
+index 8576c7b..df99125 100644
+--- a/store/types.go
++++ b/store/types.go
+@@ -69,7 +69,7 @@ func (e ErrInvalidMetadataField) Error() string {
+ //******* Groups
+
+ type Group struct {
+-       Name      string    `json:"name" gorm:"primary_key"`
++       Name      string    `json:"name" gorm:"primary_key;size:191"`
+        CreatedAt time.Time `json:"created"`
+        UpdatedAt time.Time `json:"updated"`
+ }
+@@ -169,7 +169,7 @@ type File struct {
+        ID        uint64        `json:"id" gorm:"primary_key"`
+        CreatedAt time.Time     `json:"created"`
+        UpdatedAt time.Time     `json:"updated"`
+-       GroupName string        `json:"group" gorm:"not null;index"`
++       GroupName string        `json:"group" gorm:"not null;index;size:191"`
+        Group     Group         `json:"-" gorm:"association_foreignkey:Name"`
+        Source    FileSource    `json:"source" gorm:"embedded;embedded_prefix:source__"`
+        Metadata  FileMetadata  `json:"metadata" gorm:"embedded;embedded_prefix:metadata__"`
+@@ -194,7 +194,7 @@ type Playlist struct {
+        ID        uint64          `json:"id" gorm:"primary_key"`
+        CreatedAt time.Time       `json:"created"`
+        UpdatedAt time.Time       `json:"updated"`
+-       GroupName string          `json:"group" gorm:"not null;index"`
++       GroupName string          `json:"group" gorm:"not null;index;size:191"`
+        Group     Group           `json:"-" gorm:"association_foreignkey:Name"`
+        Entries   []PlaylistEntry `json:"entries,omitempty"`
+ }
+   ```