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Halloween Special a self Post-mortem – Using MongoDB for VocZie

Halloween Special a self Post-mortem – Using MongoDB for VocZie. Chris (I’m not a ghost) Woods. What went right (with Mongo). Application design Application development and system migration Application debugging MongoDB Documentation. WWR: Application Design.

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Halloween Special a self Post-mortem – Using MongoDB for VocZie

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  1. Halloween Special a self Post-mortem – Using MongoDB for VocZie Chris (I’m not a ghost) Woods

  2. What went right (with Mongo) • Application design • Application development and system migration • Application debugging • MongoDB Documentation

  3. WWR: Application Design

  4. WWR: VocZie’s Structures • Functionality First • What data does the UI need? • What structure would best present that data? • Resulting Structures • User Object • Feed Object • Story Object • Comment Object

  5. WWR: MongoDB Structures • Collections • Objects and their identity • The two ways of relating objects • Via pointers (aka _id) • Via embedding

  6. WWR: VocZie’s Object linking • User Object • Array of pointers to feeds subscribed • Story Object • Pointer to a feed object • One embedded comment object (if available) • Comment Object • Pointer to a story object • Pointer to a user object (if available)

  7. WWR: VocZie’s Object linking User Object Feed Object 1 * 0..1 1 1 1 Story Object 1 Comment Object Comment Object 1

  8. WWR: VocZie’s REST API Examples: • /feeds/<feed_id> • /feeds/<feed_id>/stories • /feeds/<feed_id>/story/<story_id>/comments • /feeds/<feed_id>/story/<story_id>

  9. What went wrong (with Mongo)

  10. What went wrong (with Mongo) • VM is just a VM except when it is Hell… • Oh yeah, and there are no transactions • MongoDB Documentation good…. PHP Driver Documentation ..?...?

  11. WWR: The VM from Hell • VMs change over time…

  12. WWR: The VM from Hell 500 – Internal server error. There is a problem with the resource you are looking for, and it cannot be displayed.

  13. WWR: The VM from Hell root@1310-1064-2283:~# mongod mongod --help for help and startup optionsMon Jul 23 14:38:35 [initandlisten] MongoDB starting : pid=26105 port=27017dbpath=/data/db/ 64-bit** WARNING: You are running in OpenVZ. This is known to be broken!!!

  14. WWR: The VM from Hell • Have I lost all my data ? • Can I back up now?

  15. WWR: The VM from Hell • The no backup – backup… • Check out /var/lib/mongodb

  16. WWR: Transactions UpdateStoriesFromFeed( url ) if ( url is being updated ) then wait for notification else lock out everyone else from updating url fetch and parse stories from feed’s url for each story returned if ( story doesn’t already exist in DB) add story end if end for remove lock preventing anyone else from updating url end if End function

  17. WWR: Implementing a lock manually • update if current • Aka Compare and Swap • Atomic MongoDB actions allow for manual creation of locks • http://www.mongodb.org/display/DOCS/Atomic+Operations#AtomicOperations-TheABANuance

  18. Conclusions • Good • No SQL DB is great for avoiding the DAL translation pain • Aid development time • MongoDB Core Documentation is good • Bad • Small print – VM compatibility • MongoDB Driver Documentation isn’t as good as the core

  19. Q&A

  20. Who am I ? What am I doing here? • Twitter: @mcwoods • Email: woods.mc@gmail.com • Mind-Flip Blog: www.mind-flip.com/theBlog • When I think I’m being profound, or funny: www.WithBigHair.com

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