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How does data reach the disk?
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Can Applications Recover from fsync Failures?
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- 1 Intro
- 2 How does data reach the disk?
- 3 fsync is really important
- 4 It's hard to get durability correct Applications find it difficult
- 5 fsync can fail Durability gets harder to get right
- 6 Why care about fsync failures? "About a year ago the PostgreSQL community discovered that fsync (on Linux and some BSD systems) may not work the way we always thought it is [sic], with possibly disas…
- 7 Our work Systematically understand fsync failures
- 8 File System Results
- 9 Application Results
- 10 Outline
- 11 File System | Methodology: Fault Injection
- 12 File System Methodology: Workloads Common write patterns in applications • Reduced to simplest form
- 13 File System Result #1: Clean Pages Dirty page is marked clean after fsync failure on all three file systems
- 14 File System Result #22: Page Content File systems do not handle fsync errors uniformly • Page content depends on file system
- 15 File System Result #3: In-memory state In-memory data structures are not entirely reverted
- 16 Applications Five widely used applications
- 17 Applications Results: Overview Ext4 Ordered Mode
- 18 Crash/Restart Simple strategies fail Crash/restart is incorrect recovers wrong data from page cache • Example: PostgreSQL
- 19 Applications Results #1: False Failures False Failures: Indicate failure but actually succeed
- 20 Late Error Reporting All applications susceptible to data loss on ext4 data mode
- 21 Btrfs winning?
- 22 Applications Results Summary Simple strategies fail • Applications have moved away from retries
- 23 Challenges and Directions
