Crash Recovery

What is a Write-Ahead Log (WAL) and Why Do Databases Use One?

A write-ahead log (WAL) is a durability mechanism where the database records every change as a sequential log entry on stable storage before it modifies the ac…

How Does the Write-Ahead Log Enable Crash Recovery?

The write-ahead log enables crash recovery because, on restart, the database replays log records to redo committed changes that never made it to data pages, th…

What is Checkpointing in a Database and Why is it Needed?

Checkpointing is the process of periodically flushing all dirty (modified but unwritten) data pages from memory to disk and recording a marker in the write-ahe…

Redo Log vs Undo Log: What is the Difference?

A redo log records the new value produced by a change so committed effects can be reapplied after a crash, while an undo log records the old value that existed…

What is NTFS and How Does It Improve on FAT?

NTFS (New Technology File System) is Windows' journaling file system that stores nearly all metadata — including tiny files themselves — as records in a Master…

What is Journaling in a File System and Why Does It Matter?

Journaling is a technique where a file system writes a record of an intended metadata (and optionally data) change to a dedicated log before applying that chan…

What is File System Consistency Checking (fsck)?

File system consistency checking is the process of scanning on-disk metadata — inodes, directory entries, block bitmaps, and free lists — after an unclean shut…

What is a Write-Ahead Log (WAL) and Why Do Systems Use It?

A write-ahead log is an append-only file that records every change durably before it is applied to the actual data structures on disk, so a crash can never los…