26 Deal with failures 27 Idempotent operations Does not matter how many times

26 deal with failures 27 idempotent operations does

This preview shows page 26 - 37 out of 37 pages.

26
Image of page 26
Deal with failures 27
Image of page 27
Idempotent operations Does not matter how many times you execute Effect is the same as single execution All these common operations are idempotent Lookup Read ReadDir Write: since it specifies the exact offset 28
Image of page 28
Power of idempotent operations Simplify handling of failure Client sets timer, when time-out but no reply Simply retry the same request 29
Image of page 29
Non-idempotent operations These operations are not idempotent: Create (file) Remove (file) Mkdir (create directory) RmDir Error message will return from server E.g., when create is executed more than once 30
Image of page 30
Improving performance Client side Read caching Write buffering Similar to standalone file system Unique change: cache consistency problem Due to multiple caches in several clients 31
Image of page 31
Cache consistency problems C2 updates file F to version 2: F[v2], but does not commit it to server when it closes the file Problems: update visibility & stale cache 32
Image of page 32
Update visibility problem C3 reads F from server, got old content 33
Image of page 33
Stale cache problem F[v2] finally flushed to server, but now caches C1 (& C3) are stale 34
Image of page 34
Solution: flush-on-close Client flushes all updates to server when file is closed Solve the update visibility problem 35 flush-on-close
Image of page 35
Solution: cache validation Client checks if cache is current by issuing GETATTR to server before opening/accessing the file 36 Getattr
Image of page 36
References NFS: Network File System Protocol Specification 37
Image of page 37

You've reached the end of your free preview.

Want to read all 37 pages?

  • Fall '14

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes