Interview Questions
1. What is Halloween protection?
“Halloween protection” in database systems refers to a solution for a problem that can occur in update queries. The
problem occurs when an update itself affects the rows selected for update. For example, imagine a company wants to give
every employee a 10% pay increase. If the update query is unlucky enough to walk the salary index then the same row may be
selected, updated, the update moves the row ahead in the index, and then the row will be redundantly selected again and
again. This problem is corrected by isolating the rows chosen from the effects of the update itself.
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