IPA IP 2026 Question 86
A question IPA Japan published in 令和8年度 ITパスポート試験 公開問題 問86, translated into English. ITPEC is based on the same exams.
In preparation for database failures, backup files are made every day after closing time. A full backup file is made every Saturday, and a differential backup file is made from Sunday through Friday. A differential backup file means a backup file of all the differential data from the last full backup file up to the day on which the differential backup file is made. Because the database was damaged on a Wednesday, a decision was made to restore the database to the state at the closing time on Tuesday, the previous day. Which of the following is the minimum set of backup files required to restore the database?
Explanation
Saturday's full backup and Tuesday's differential backup — a differential file already holds every change since the last full backup.
- •Saturday full backup: the whole database as of Saturday closing, the base
- •Sunday differential: changes since Saturday
- •Monday differential: changes since Saturday (Sunday's and Monday's)
- •Tuesday differential: changes since Saturday (Sunday's, Monday's and Tuesday's)
Restore Saturday's full backup, then apply Tuesday's differential file: the database is back to its state at Tuesday closing. Sunday's and Monday's files add nothing that Tuesday's does not already contain.
Answer (d)
Why not others:
- •(a) and (b) — no full backup: differential files hold only changed data, so everything unchanged since Saturday could not be restored
- •(c) — restores correctly, but Sunday's and Monday's files are redundant, so it is not the minimum
Key rule: Differential backup restores as full + the latest differential only; incremental backup restores as full + every incremental in order.
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This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.