9 things you need to know about Write Ahead Logging: 1. Write-Ahead Log (WAL): A critical component in database systems that ensures data durability even when servers fail unexpectedly. 2. Basic concept: Before modifying data, the intended changes are recorded in a log file. This log serves as a recovery mechanism in case of system crashes. 3. Implementation: Each server process maintains a single, sequentially appended log. Entries are given unique identifiers to aid in log management and operations. 4. Structure: A typical log entry contains an index, the actual data, entry type, and a timestamp. 5. Recovery process: Upon restart, the system can reconstruct its state by reading and replaying the log entries. 6. Key consideration: Balancing between immediate disk writes for maximum durability and delayed writes for better performance. 7. Data integrity: Techniques like CRC records or end-of-entry markers are used to detect corrupted log entries during recovery. 8. Log management: As logs grow, strategies like segmented logs and low-water marks become necessary for efficient storage use. 9. Transactional support: WAL facilitates atomic updates, serving as a foundation for ACID-compliant databases. Bonus: You can watch the video I created this year to understand Write Ahead Logging pattern. Link in the comments. Bonus++ : I am bringing more videos soon on WAL formats within systems like Cassandra, RocksDB, SQLite etc. stay tuned.

Write-ahead-logging youtu.be/yV_Zp0Mi3xs

@thegeeknarrator That's the best complimentary content when reading DDIA.

@thegeeknarrator WAL stores the previous state of the data before the modifcation as well?Say as a part of the transaction a counter is incremented in a table and some other table is also modified.(1/2)

@thegeeknarrator Bullshit . Please implement a journal on raw block device . It should not be more than 200MB on 2 TB disk