Several CS issues here:

* `public static function` should be used
* Extra space between parenthesis (both in function prototype and `new SQLIImportLogger()`
* `{` should be on next line (either for function or condition)

Moreover, please don't use `$GLOBALS` for singleton. Use a private or protected static property instead. Much more readable.
If you use a property, you won't have the need to test its existence with `isset()` (`null` by default).