Book that is currently not available - alternative

[ccristian]

"When a patron tires to place on hold a book that is currently not available it should not be possible, thus resulting in book hold failed event, as it is depicted below"

The book view should not let the patrol to hold only available books ?
(grey out the others etc)

In this way will be impossible to to hold a book that is not available ....

[pilloPl]

Yes, but also that means that we would have to pessimimisticaly lock everything degrading scalability

If you are looking at the rendered view of available books you are doing it for a moment. In this moment someone else could have gotten the book.