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Tentative Updates in MINO

Tentative Updates in MINO. Steven Czerwinski Jeff Pang Anthony Joseph John Kubiatowicz ROC Winter Retreat January 13, 2002. MINO: Mail service on OceanStore. Enables mail storage and access Individual user accounts with INBOX and folders Send e-mail through SMTP proxy

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Tentative Updates in MINO

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  1. Tentative Updates in MINO Steven Czerwinski Jeff Pang Anthony Joseph John Kubiatowicz ROC Winter Retreat January 13, 2002

  2. MINO: Mail service on OceanStore • Enables mail storage and access • Individual user accounts with INBOX and folders • Send e-mail through SMTP proxy • Read and organize e-mail through IMAP proxy • Interesting application for OceanStore • Mail needs global scale and mobility • Tested client APIs and tentative updates • It’s not a file system UnmodifiedMail Client MINO Global ScaleMail Service AccessPoint (Berkeley) AccessPoint (Tahoe) Send e-mail toczerwin@ostore Read new message, Move to OceanStore folder

  3. Folder Object MessageObject OceanStore Client API AccessPoint Inner RingNodes Mail Object Layer IMAP Proxy SMTP Proxy • MINO builds on OceanStore • Defines message, folder, mail drop objects • Access point is OceanStore client to support legacy protocols • Access point typically runs on client machine The MINO architecture Object • OceanStore provides object store access • Inner Ring commits updates, Replicas cache objects ClientNode Replica Nodes OceanStore

  4. Client ReplicaNodes Adapting to mobility What happens when we go to Tahoe? • Replicas of our mail objects migrate towards us • Updates (writes) must still go to inner ring • Inner ring is bottle neck to adaptability • Can choose replicas based on conditions, but not inner ring • Commit time = Ttransmit to IR + Tin queue + Tprocess update Berkeley Granlibakken Internet InnerRingNodes

  5. SaveTentative Saved (4 responses) Commit update Completed Removing the bottleneck • Use relaxed consistency & tentative updates • Don’t wait for the inner ring response • Consider updates tentatively committed when received by n of m replicas • Provides durability • Mail layer uses application-specific logic to resolve conflicts Replica Nodes Inner RingNodes Move Msg MailObject Layer IMAP Proxy

  6. Update Request Action: Replace Data Predicate: Version = 5 Update failed, version = 6 Folder Object Reapply action Object Data Pending Actions Update Request #2 Action: Replace Data Predicate: Version = 5 • Submits update, predicated on version • On failure, client is notified and reads newest • Checks pending actions for true conflict, then reapplies • Resubmits with new predicate Conflict detection and resolution Inner Ring Nodes Client • Client tracks pending actions

  7. Benchmarking Client • Analyzed benefits to mobile clients • IMAP login benchmark • Authentication, client sync, and fetches new msgs • 8 blocking IMAP commands • Trace from Mozilla 1.0 IMAP client • Experiment • Account with 100 msgs (3 new) and 50 folders • 50 trials run for each artificial latency value • Cases: no tentative, tentative, tentative w/ warm caches ArtificialLatency Inner Ring Nodes ReplicaNodes

  8. Results Tentative updates more robust to increases in latency!

  9. Unresolved issues • How do we pick remote replicas? • Failures should be independent • Need at least one well-behaved remote replica • Failure rate affects choosing n and m • How do we know when to use tentative? • Tentative benefits when IR slow or far away • Puts load on infrastructure resources (replicas) • What criteria are we trying to optimize? • Investigating introspection to address issues

  10. Conclusions • Fully functional mail service with OceanStore • Works with unmodified mail clients • Supports IMAP and SMTP access • Investigated tentative commits in OceanStore • Client API sufficient to support conflict resolution • Showed improvement for mobile clients • Made suggestions for next prototype • Future work • Using introspection to make optimization decisions • Sharing tentative updates with other sessions

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