The backup that disappeared was one of six on the shelf. Another card changed places. Which one is missing?
A backup shelf is one of those places where a quick glance can lie. A row of boxes looks complete until the day you need one particular box. This is a paper puzzle, not a claim about any real backup system, but the feeling is familiar.
The upper shelf is BEFORE. The lower shelf is AFTER. Both show three positions in each of two rows. One card moved to a different position and one card disappeared. Your job is to name the card that is missing. The question mark tells you where there is a gap, but it does not tell you the name of the missing card. Compare the names, not just the positions.
Try it without writing the list down. If you find yourself counting slots instead of reading labels, that is exactly the trap. The six-card layout was kept large enough to read on a phone, so no magnifying glass is required.
The Backup That Disappeared: The Answer
LOG 3 is missing. The BEFORE shelf has FULL 1, FULL 2, DIFF 1, LOG 1, LOG 2 and LOG 3. The AFTER shelf has the first five of those names, with LOG 2 and FULL 2 in different places. The empty slot is a distraction: a moved card can make a different card seem absent if you only compare positions.
A useful way to solve it is to make a set of names. In this little world, BEFORE minus AFTER equals LOG 3. That is more reliable than saying, ‘the second card moved, so that must be the problem.’
In a real restore, the question is not whether a shelf looks full. It is whether the required backup files exist, form the chain you expect, and can actually be restored. A neat filename is a promise made by a human. A successful restore test is evidence.
I like this puzzle because the answer is simple after you slow down. The difficult part is refusing to let the layout do the counting for you. If a teammate picked FULL 2, show them the AFTER shelf again. It is there, just not where it began.
Published by Pinal Dave on SQLAuthority. More of my work at pinaldave.com.
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