LC

Understand fsync, I/O Barriers, and Disk Write Ordering

medium10/10

Implement Copy-on-Write Filesystem for SnapshotsNext

Language

Compiler

2.0s Limit 256MB

Implementation

Demonstrate fsync and I/O barriers.

Requirements:

Write data to file
Use fsync() to ensure data on disk
Demonstrate write ordering with barriers
Show difference between buffered and sync writes
Measure fsync() latency
Explain crash recovery scenarios
Use O_DIRECT or O_SYNC for comparison

Test:

Write data with and without fsync
Measure write latency
Show fsync() waiting for disk
Demonstrate write ordering

Why This Matters

SQLite and Postgres both rely on fsync() plus write ordering to guarantee that a committed transaction survives a power loss, and both batch writes into a single fsync (group commit) because one fsync on spinning disk can cost 5-20 milliseconds. Skipping the barrier between two dependent writes is exactly how the classic 'transfer $100, crash mid-way, money disappears' bug happens in real financial software.

Hints

0 / 3 revealed

Validation Suite

main.c

Workspace 1.0