there are multiple Database storage engines in MySQL. MyISAM and InnoDB for example.
MyISAM locks the whole table on single write and can be corrupted etc.
InnoDB locks only the row not the whole table and has no chances of corruption (as far as i know)
first of all, NEVER PASTE YOUR DATABASE PASSWORD. Replace it with something like XXXX. Secondly use jQuery or something like that and thirdly nothing would show up because you're using mysqli_fetch_array and using string keys.
You might want to replace it with mysqli_fetch_assoc