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Advanced Topic 35 of 51 Databases

Recovery and Logging

Write-ahead logs restoring state after failure.

How it works

Databases recover from crashes using a write-ahead log: every change is recorded in a sequential log and flushed to disk before the data pages are modified or the transaction commits. After a failure, recovery algorithms such as ARIES analyze the log, redo committed work that did not reach disk and undo uncommitted work. Checkpoints limit how much log must be replayed. Backups plus archived logs allow point-in-time recovery.

Step-by-step walkthrough

  1. A change is first written to the write-ahead log.
  2. Only then is the commit acknowledged.
  3. Data pages are flushed to disk later.
  4. After a crash the log is replayed to redo committed work.
  5. Uncommitted changes are undone.

Where it is used

Every serious database uses logging to deliver durability and atomicity, and replication systems ship the log to replicas.

Common pitfall

Disabling fsync or using volatile caches risks data loss on power failure. Log files that fill the disk can halt the database. Backups that were never tested may not restore. Plan retention, monitor replication lag and practice restore drills. Remember that logical dumps and physical backups have different recovery speeds and guarantees.

Where it fits in the course

Recovery and Logging is topic 35 of 51 in Databases, rated Advanced. It follows Common Table Expressions. The next topic is Database Partitioning.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Databases quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Recovery and Logging?
Write-ahead logs restoring state after failure. It belongs to Databases and is an advanced-level topic.
Where do people use Recovery and Logging?
Every serious database uses logging to deliver durability and atomicity, and replication systems ship the log to replicas.
What is the most common mistake with Recovery and Logging?
Disabling fsync or using volatile caches risks data loss on power failure.
What should I learn before this topic?
Start with Common Table Expressions, the topic just before it in Databases.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Databases quiz.
Is Recovery and Logging hard to learn?
It is an Advanced topic. Expect to read the explanation more than once and to connect it with earlier topics. Working through a small example by hand helps most.
How long does it take to learn Recovery and Logging?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Recovery and Logging?
Common Table Expressions, Database Partitioning, Window Functions are closely connected. The full list is in the related topics section of this page.
What should I study after Recovery and Logging?
Continue with Database Partitioning, the next topic in Databases.

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