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Backup & Recovery — Junior

At junior level, focus on this question:

What's the difference between a full and an incremental backup, and why not just take a full backup every time?

Full backups

A full backup copies the entire database's data at a point in time — the most complete, simplest thing to restore from (just load it back), but also the slowest to take and the most storage-hungry, especially if you keep several.

flowchart LR Sun["Sunday: full backup\n(500 GB)"] Mon["Monday: full backup\n(500 GB again)"] Tue["Tuesday: full backup\n(500 GB again)"] Sun --- Mon --- Tue

Taking a full backup every day means storing (and copying) the entire dataset every single day — most of which hasn't changed since yesterday.

Incremental backups

An incremental backup captures only what's changed since the last backup (full or incremental), which is dramatically smaller and faster to take for a large, slowly-changing dataset.

flowchart LR Full["Sunday: FULL backup\n(500 GB)"] --> Inc1["Monday: INCREMENTAL\n(only changes: 5 GB)"] Inc1 --> Inc2["Tuesday: INCREMENTAL\n(only changes: 4 GB)"]

The trade-off: restoring now requires the full backup plus every incremental since it, applied in order — more steps, more places something could go wrong, and typically a slower restore than a single full backup would give you.

Full backup Incremental backup
Backup time/storage High, every time Low, after the first full
Restore time Fast — one file to load Slower — full + chain of incrementals, applied in sequence
Failure surface One backup to trust Every incremental in the chain must be intact

🎓 Takeaway: full backups are simple and safe to restore from but expensive to take repeatedly; incremental backups are cheap to take but require a longer, more fragile chain to restore. Most real systems combine both — a periodic full backup, with incrementals in between (this is middle.md's subject, taken to its logical extreme with continuous logs).

Test yourself

  1. If Tuesday's incremental backup is corrupted, what happens to your ability to restore to Wednesday, even if Wednesday's own incremental is fine?
  2. Why does an incremental backup strategy need at least one full backup to ever be useful?
  3. For a database that changes very little day-to-day (mostly reference data), would full or incremental backups make more sense as the primary strategy? Why?

Continue to middle.md.