[mjb]

The answer to most of your questions is 'maybe', unfortunately. Reasoning about the things that could happen when memory errors occur is very difficult, because they occur outside the mental model of computation that most programmers (and systems administrators) use.

Let's use MySQL as an example. A bit flip in the memory which holds the code may cause it to crash. A bit flip in the 'metadata' could cause the table to become corrupted, potentially recoverably. A bit flip in the data itself could turn 'Travis' into 'Trbvis', which might go undetected depending on where it happened and which storage engine you are using.

The use of memory for OS page caching (less so in databases, which often use O_DIRECT and more so in other programs) means that arbitrary corruption could happen to pieces of disk data your program didn't even touch, if you touch data near them.