Prophet - A peer to peer replicated disconnected database

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A semirelational, …

A semirelational,
peer to peer replicated,
disconnected, versioned,
property database with
self-healing conflict resolution, as presented at YAPC::Asia 2008

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  • 1. Step 3: Prophet jesse@bestpractical.com clkao@bestpractical.com Friday, May 16, 2008 1
  • 2. Cloud computing is Sharecropping. ( ) Friday, May 16, 2008 2
  • 3. Chia-liang Kao Friday, May 16, 2008 3
  • 4. Jesse Vincent Friday, May 16, 2008 4
  • 5. We work together Friday, May 16, 2008 5
  • 6. CL lives in Taipei Jesse lives in Boston Friday, May 16, 2008 6
  • 7. Sometimes we need to work face to face Friday, May 16, 2008 7
  • 8. TPE~BOS: 9410 mi TPE-HNL: 5,095 mi BOS-HNL: 5,069 mi Friday, May 16, 2008 8
  • 9. Our Plan Step 1: Go to Hawaii for “work” Step 2: ??? Step 3: Prophet! Friday, May 16, 2008 9
  • 10. The Plan Backfired We were there for 8 days We wrote 8000 lines of Perl We figured out step 2 Friday, May 16, 2008 10
  • 11. Step 2: Build a Disconnected Syncable Database Friday, May 16, 2008 11
  • 12. Prophet Friday, May 16, 2008 12
  • 13. Prophet A semirelational, peer to peer replicated, disconnected, versioned, property database with self-healing conflict resolution Friday, May 16, 2008 13
  • 14. Bribery! Two tshirts. If you write a (real) patch for Prophet during this talk, you get a tshirt. Send patches to jesse@bestpractical.com Friday, May 16, 2008 14
  • 15. Getting Prophet Prophet http://code.bestpractical.com/bps-public/Prophet/ SD http://code.bestpractical.com/bps-public/sd/ Friday, May 16, 2008 15
  • 16. What do all those buzzwords mean? Friday, May 16, 2008 16
  • 17. semirelational Joins are expensive No backend Join support (yet) Friday, May 16, 2008 17
  • 18. peer-to-peer replicated Update any replica Pull from any replica Push to any replica Publish a replica Changes will propagate Friday, May 16, 2008 18
  • 19. disconnected Real-time replication is hard to scale It only works in the cloud I don't live in the cloud I want my data when I'm offline Prophet sync can happen whenever Friday, May 16, 2008 19
  • 20. versioned Compare a record to any point in the past All changes fully logged Undo changes Use history to be smart Friday, May 16, 2008 20
  • 21. property database Atomic operations CREATE, READ, UPDATE, DELETE, SEARCH Record types can have optional validation and canonicalization Records of the same type do not need to have the same properties Add and remove properties at will Friday, May 16, 2008 21
  • 22. self-healing conflict resolution Remembers all conflict resolutions Syncs all resolutions with your peers Detects identical conflicts Uses your peers’ resolutions to “vote” for the winner of a conflict Friday, May 16, 2008 22
  • 23. What could you build with Prophet? Friday, May 16, 2008 23
  • 24. sd A bug tracker: “simple defects” • id. Status, Summary • History • Comments • Attachments Friday, May 16, 2008 24
  • 25. ./bin/sd ticket create --summary quot;Can't sync sd with Google Codequot; --status new Created ticket 93BF979E-08C1-11DD-94C3-D4B1FCEE7EC4 Friday, May 16, 2008 25
  • 26. ./bin/sd ticket search --regex . 93BF979E-08C1-11DD-94C3-D4B1FCEE7EC4 Can't sync sd with Google Code new Friday, May 16, 2008 26
  • 27. ./bin/sd ticket update --uuid 93BF979E-08C1-11DD-94C3-D4B1FCEE7EC4 --status resolved ./bin/sd ticket search --regex . 93BF979E-08C1-11DD-94C3-D4B1FCEE7EC4 Can't sync sd with Google Code resolved Friday, May 16, 2008 27
  • 28. Bugs on my laptop aren’t interesting. Friday, May 16, 2008 28
  • 29. Syncable! Jesse ./bin/sd publish /tmp/mybugs scp -rvp /tmp/mybugs my.com:public_html/sd CL ./bin/sd pull prophet:http://my.com/~jesse/sd Friday, May 16, 2008 29
  • 30. My project has a bug tracker Friday, May 16, 2008 30
  • 31. My project has a bug tracker Actually, mine use two: • RT • hiveminder.com Friday, May 16, 2008 30
  • 32. Foreign Replicas Prophet makes Foriegn Replicas easy SD gets them quot;for freequot; Friday, May 16, 2008 31
  • 33. Wrote an RT Replica for SD (Using only the public REST API) It took an afternoon Mirror an RT instance into SD Share it with your peers using prophet Sync changes back from your peers to RT Supports Comments and Attachments Friday, May 16, 2008 32
  • 34. ...and one for Hiveminder (Using only the public REST API) Friday, May 16, 2008 33
  • 35. I can sync my bugs with RT or Hiveminder Friday, May 16, 2008 34
  • 36. Actually, it’s better Friday, May 16, 2008 35
  • 37. I can sync between RT and Hiveminder Friday, May 16, 2008 36
  • 38. I can sync between two different RTs, too Friday, May 16, 2008 37
  • 39. We need more replica definitions: • • Trac GNATS • • Google Code What else? • SourceForge • Bugzilla • Jira • GForge • debbugs Friday, May 16, 2008 38
  • 40. What can you use Prophet for? Friday, May 16, 2008 39
  • 41. All your “little” databases Friday, May 16, 2008 40
  • 42. All the databases you want while offline. • • CRM Blog • Bug tracking • Trading Card Database • Sales orders • Ideas? • Phone book Friday, May 16, 2008 41
  • 43. “Private” Social Networks How about a P2P BBS? Prophet doesn’t need a server. You can sync over sneakernet. Friday, May 16, 2008 42
  • 44. A look inside Prophet Friday, May 16, 2008 43
  • 45. Terms and Concepts • • Database Property Change • • Database Replica Conflict • • “Foreign” Replica Resolution • • Record Nullifcation Change Set • • Record Type Resolution Change Set • • Change Set Merge • • Change Merge Ticket Friday, May 16, 2008 44
  • 46. Database Backends Friday, May 16, 2008 45
  • 47. The Record Store Stores indivdual records by type Friday, May 16, 2008 46
  • 48. The Changeset Store Stores each atomic change to a set of records Replaying all changesets will create an exact clone of the replica Friday, May 16, 2008 47
  • 49. Native Replica Types Friday, May 16, 2008 48
  • 50. Subversion Slow Steady Robust Supports remote sync Requires Subversion Perl Bindings Friday, May 16, 2008 49
  • 51. Filesystem Readable Flat files Compact Fast (Not yet fully atomic) Friday, May 16, 2008 50
  • 52. HTTP Designed to let you “publish” databases Flat-files, Currently read-only. Same format as the filesystem replica type. Friday, May 16, 2008 51
  • 53. “Foreign” replicas Will usually be app specific All current examples are in SD Friday, May 16, 2008 52
  • 54. Synchronization Friday, May 16, 2008 53
  • 55. Publish Serialize and export all of a replica's resolutions and changesets Friday, May 16, 2008 54
  • 56. Pull Integrate unseen resolutions and then unseen changesets from a replica Friday, May 16, 2008 55
  • 57. Push Integrate new resolutions and changesets into a replica Friday, May 16, 2008 56
  • 58. Resolving Conflicts Figures out the best resolution “Nullifies” the conflict so the changeset can be cleanly integrated Integrates the conflicting changeset Records the resolution as a new changeset Records the resolution decision in the resolution database Friday, May 16, 2008 57
  • 59. “The Best Resolution” Prophet has clever ways to figure out the best resolution. If there are previous resolutions for the same conflict and a majority agree, use that If the merger has specified a “prefer this side” choice, use that Prompt the user to make a decision, giving them info about previous decisions for this conflict Friday, May 16, 2008 58
  • 60. We don't have a proof for the algorithm yet We do have dozens of runs of randomized testing. So far, it always stabilizes sanely. Friday, May 16, 2008 59
  • 61. How does it scale? Vertical scale is boring Designed to scale to many peers You are not Google Current target is databases of O(50k) records Friday, May 16, 2008 60
  • 62. How does it scale? Vertical scale is boring Designed to scale to many peers You are not Google Does anyone here work for Google? Current target is databases of O(50k) records Friday, May 16, 2008 60
  • 63. Why not, then? We just have a political agenda. Web 2.0 is not Open Source. Your data shouldn’t be ‘exportable’ from the cloud. You should always have full control. So we dont need to store 10 billion records in one database. Friday, May 16, 2008 61
  • 64. (Do you have 10 billion bugs, customer contacts or sales orders?) Friday, May 16, 2008 62
  • 65. That said, we'd love to see a scalable, high performance prophet replica store Friday, May 16, 2008 63
  • 66. Project Status Simple, well-defined Perl API RESTy web API (with microserver) Fast, lightweight backend Small, active dev community Great test coverage Horrible POD coverage Friday, May 16, 2008 64
  • 67. Our Plans Improved search and indexing (Including full-text indexing) Query language Proper security model Jifty, Catalyst, Rails models? Friday, May 16, 2008 65
  • 68. Prophet is very young Many, many hours of design About 10 days of two hackers hacking Friday, May 16, 2008 66
  • 69. Codebase Prophet 5479 lines of code and doc 1693 lines of tests sd 1695 lines of code and doc 876 lines of tests Friday, May 16, 2008 67
  • 70. Getting Prophet Prophet http://code.bestpractical.com/bps-public/Prophet/ SD http://code.bestpractical.com/bps-public/sd/ Friday, May 16, 2008 68
  • 71. Getting Involved prophet-subscribe@lists.bestpractical.com #prophet on freenode IRC Friday, May 16, 2008 69
  • 72. Thanks! Friday, May 16, 2008 70