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Slides from my talk at MongoDB Boston 2013 on moving an application from a relational database to MongoDB. I discussed challenges and lessons learned from this project.

Slides from my talk at MongoDB Boston 2013 on moving an application from a relational database to MongoDB. I discussed challenges and lessons learned from this project.

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  • 1. No More SQL A chronicle of moving a data repository from a traditional relational database to MongoDB Glenn Street Database Architect, Copyright Clearance Center
  • 2. Who am I? ● Database Architect at Copyright Clearance Center ● Oracle Certified Professional ● Many years of database development and administration ● Learning to embrace “polyglot persistence” ● Been working with MongoDB since version 1.6
  • 3. What is Copyright Clearance Center? "Copyright Clearance Center (CCC), the rights licensing expert, is a global rights broker for the world’s most sought-after books, journals, blogs, movies and more. Founded in 1978 as a not-for-profit organization, CCC provides smart solutions that simplify the access and licensing of content. These solutions let businesses and academic institutions quickly get permission to share copyright-protected materials, while compensating publishers and creators for the use of their works." www.copyright.com
  • 4. What I want to talk about today ● ● ● Not application design, but data management issues Our experience in moving from "legacy" relational data way of doing things These experiences come from one large project
  • 5. What do I mean by “data management”? ● Topics like naming conventions, data element definitions ● Data modeling ● Data integration ● Talking to legacy (relational) databases ● Archive, purge, retention, backups
  • 6. Where we started ● 200+ tables in a relational database ● Core set of tables fewer, but many supporting tables ● 2.5 TB total (including TEMP space, etc.) ● Many PL/SQL packages and procedures ● Solr for search
  • 7. Today ● ● ● We use MongoDB in several products The one I'll talk about today is our largest MongoDB database (> 2 TB) Live in production end of September
  • 8. What options did we have in the past for horizontal scaling? ● At the database layer, few ● Clustering ($$) ● So, we emphasized scaling at the application tier ● We wanted to be able to scale out the database tier in a low-cost way
  • 9. What kind of data? ● "Work" data, primarily books, articles, journals ● Associated metadata – Publisher, author, etc.
  • 10. Application characteristics ● ● Most queries are reads via Solr index Database access is needed for additional metadata not stored in Solr ● Custom matching algorithms for data loads ● Database updates are done in-bulk (loading) ● Loads of data come from third-party providers ● On top of this we've built many reports, canned and ad-hoc
  • 11. Here's what the core data model looked like: highly normalized
  • 12. Where we are today ● ● 12 MongoDB shards x 200 GB (2.4 TB) MongoDB database Replica sets, including hidden members for backup (more about that later) ● GridFS for data to be loaded ● MMS for monitoring ● JEE application (no stored procedure code) ● Solr for search
  • 13. What motivated us? ● ● Downtime every time we made even the simplest database schema update The data model was not appropriate for our use case – Bulk loading (very poor performance) – Read-mostly (few updates) – We want to be able to see most of a "work's" metadata at once – This lead to many joins, given our normalized data model
  • 14. More motivators ● ● ● ● Every data loader required custom coding The business users wanted more control over adding data to the data model “on-the-fly” (e.g., a new data provider with added metadata) This would be nearly impossible using a relational database MongoDB's flexible schema model is perfect for this use!
  • 15. What were our constraints? ● ● ● Originally, we wanted to revamp the nature of how we represent a work Our idea was to construct a work made up of varying data sources, a “canonical” work But, as so often happens, time the avenger was not on our side
  • 16. We needed to reverse-engineer functionality ● ● ● ● This meant we needed to translate the relational structures We probably didn't take full advantage of a documentoriented database The entire team was more familiar with the relational model Lesson: – Help your entire team get into the polyglot persistence mindset
  • 17. We came up with a single JSON document ● We weighed the usual issues: – ● Embedding vs. linking Several books touch on this topic, as does the MongoDB manual – One excellent one: MongoDB Applied Design Patterns by Rick Copeland, O'Reilly Media.
  • 18. We favored embedding ● ● "Child" tables became "child" documents This seemed the most natural translation of relational to document ● But, this led to larger documents ● Lesson: – We could have used linking more
  • 19. Example: one-to-one relationship
  • 20. In MongoDB work... "publicationCountry" : { "country_code" : "CHE", "country_description" : "Switzerland" }
  • 21. Example: one-to-many relationship
  • 22. In MongoDB An array of “work contributors” "work_contributor" : [ { "contributorName" : "Ballauri, Jorgji S.", "contributorRoleDescr" : "Author", }, { "contributorName" : "Maxwell, William", "contributorRoleDescr" : "Editor", },... ]
  • 23. When embedding... ● ● ● Consider the resulting size of your documents Embedding is akin to denormalization in the relational world Denormalization is not always the answer (even for RDBMS)!
  • 24. Data migration from our relational database ● ● ● Wrote a custom series of ETL processes Combined Talend Data Integration and custom-built code Also leveraged our new loader program
  • 25. But...we still had to talk to a relational database ● ● The legacy relational database became a reporting and batchprocess database (at least for now) Data from our new MongoDB system of record needed to be synced with the relational database – ● Wrote a custom process to transform the JSON structure back to relational tables Lesson: – Consider relational constraints when syncing from MongoDB to a relational database ● We had to account for some discrepancies in field lengths (MongoDB is more flexible)
  • 26. More Lessons Learned ● ● Document size is key! The data management practices you're used to from the relational world must be adapted; example: key names ● In the relational world, we favor longer names ● We found that large key names were causing us pain – We're not the first: see “On shortened field names in MongoDB” blog post – But, this goes against “good” relational database naming practices (e.g., longer column names are self-documenting)
  • 27. More Lessons Learned ● Our way of using Spring Data introduced it's own problems – ● “scaffolding” Nesting of keys for flexibility was painful Example: workItemValues.work_createdUser.rawValue
  • 28. Backups at this scale are challenging! ● Mongodump and mongoexport were too slow for our needs ● Decided on hidden replica set members on AWS ● Using filesystem snapshots for backups ● Looking into MMS Backup service
  • 29. Another Lesson: Non/SemiTechnical Users ● For example, business analysts, product owners ● Many know and like SQL ● Many don't understand a document-oriented database ● Engineering spent a lot of time and effort in raising the comfort level – ● This was not universally successful An interesting project, SQL4NoSQL
  • 30. How to communicate structure?
  • 31. Communicating Structure ● Mind map was helpful initially ● Difficult to maintain
  • 32. JSON Schema {"$schema": "http://json-schema.org/draft-03/schema", "title": “Phase I Schema", "description": "Describes the structure of the MongoDB database for Phase I", "type":"object", "id": "http://jsonschema.net", "required":false, "properties":{ "_id": { "type":"string", "required":false }, ...
  • 33. JSON Schema for communicating structure ● I created a JSON schema representation of the “work” document – – ● ● JSON Schema JSON Schema.net Was used by QA and other teams for supporting tools JSON Schema also useful, but also cumbersome to maintain
  • 34. Next Steps/Challenges ● Investigating on-disk (file system) compression – ● Very promising so far Can we be more "document-oriented"? – Remove vestiges of relational data models ● Implement an archiving and purging strategy ● Investigating MMS Backup
  • 35. Vote for these JIRA Items! ● “Option to store data compressed“ ● “Bulk insert is slow in sharded environment” ● “Tokenize the field names” ● “Increase max document size to at least 64mb” ● “Collection level locking”
  • 36. Thanks! ● Twitter: @GlennRStreet ● Blog: http://glennstreet.net/ ● LinkedIn: http://www.linkedin.com/in/glennrstreet/