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DOCS Add guide on new MySQL collation to Server Reqs

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This was previously documented in the 4.7.0 changelog, but will be an ongoing
concern for developers, so it makes sense to replicate in a more obvious place.
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Garion Herman 2021-02-24 15:38:55 +13:00
parent 5a4641d806
commit 34bc080515
1 changed files with 14 additions and 1 deletions
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15
docs/en/00_Getting_Started/00_Server_Requirements.md
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@ -28,7 +28,20 @@ Use [phpinfo()](http://php.net/manual/en/function.phpinfo.php) to inspect your c
* SQL Server ([third party module](https://addons.silverstripe.org/add-ons/silverstripe/mssql), community supported)
* SQLite ([third party module](https://addons.silverstripe.org/add-ons/silverstripe/sqlite3), community supported)
### Connection mode (sql_mode) when using MySQL server >=5.7.5
### Default MySQL Collation
In Silverstripe CMS Recipe 4.7 and later, new projects default to the `utf8mb4_unicode_ci` collation when running against MySQL, which offers better support for multi-byte characters such as emoji. However, this may cause issues related to Varchar fields exceeding the maximum indexable size:
- MySQL 5.5 and lower cannot support indexes larger than 768 bytes (192 characters)
- MySQL 5.6 supports larger indexes (3072 bytes) if the `innodb_large_prefix` setting is enabled (but not by default)
- MySQL 5.7 and newer have `innodb_large_prefix` enabled by default
- MariaDB ~10.1 matches MySQL 5.6's behaviour, >10.2 matches 5.7's.
You can rectify this issue by upgrading MySQL, enabling the `innodb_large_prefix` setting if available, or reducing the size of affected fields. If none of these solutions are currently suitable, you can remove the new collation configuration from `app/_config/mysite.yml` to default back to the previous default collation.
Existing projects that upgrade to Recipe 4.7.0 will unintentionally adopt this configuration change. Recipe 4.7.1 and later are unaffected. See [the release notes](/changelogs/4.7.0/#default-mysql-collation-updated) for more information.
### Connection mode (sql_mode) when using MySQL server >=5.7.5
In MySQL versions >=5.7.5, the `ANSI` sql_mode setting behaves differently and includes the `ONLY_FULL_GROUP_BY` setting. It is generally recommended to leave this setting as-is because it results in deterministic SQL. However, for some advanced cases, the sql_mode can be configured on the database connection via the configuration API (see `MySQLDatabase::$sql_mode` for more details.) This setting is only available in Silverstripe CMS 4.7 and later.