MongoDB to Cassandra

MetaBroadcast's presentation at the Cassandra Meetup, by Fred van den Driessche, Tom McAdam, Adam Horwich.
Dec. 10th 2012

1. MongoDB to Cassandra The Atlas Odyssey Fred van den Driessche Engineer @fredvdd Tom McAdam CTO @tfm Adam Horwich Systems Engineer @Mmmkayness
3. http://flickr.com/photos/dhammza/88644497/
4. tbc Video and audio metadata from 20+ sources Profiles and activity from video and audio products, social networks Our platform - late 2012 tbc MetaBroadcast platform Analytic requests and groupings
5. ?
6. Main clients Main Partners Data Partners
7. What is Atlas? ATLAS DB BBC PA C4 etc... /content /schedules /topics sitemaps radioplayer interlinking
8. DEMO
9. Atlas Data Model brand item series version broadcast location
10. MongoDB • flexible • features • really simple • shell
11. Where MongoDB falls short • too simple • lack of control • sharding • embedding
12. Where to?
13. Where to? • add a cache?
14. Atlas API • content • http://atlas.metabroadcast.com/3.0/content.json?uri=http://www.bbc.co.uk/programmes/ b0074g7p&annotations=description,brand_summary,locations&apiKey=6ed2a984627daff816198acde82 • http://atlas.metabroadcast.com/3.0/content.json?apiKey=aaaa&uri=http://www.bbc.co.uk/programmes/ b0074g7p&annotations=description,brand_summary,locations • schedules • http://atlas.metabroadcast.com/3.0/schedule.json?from=now&to=now.plus. 3h&channel=bbcone&publisher=bbc.co.uk • http://atlas.metabroadcast.com/3.0/schedule.json? from=1948-12-24&to=1948-12-25&channel=radio4&publisher=bbc.co.uk • api explorer http://atlas.metabroadcast.com/#apiExplorer
16. Atlas API • content • http://atlas.metabroadcast.com/3.0/content.json?uri=http://www.bbc.co.uk/programmes/ b0074g7p&annotations=description,brand_summary,locations&apiKey=6ed2a984627daff816198acde82 • http://atlas.metabroadcast.com/3.0/content.json?apiKey=aaaa&uri=http://www.bbc.co.uk/programmes/ b0074g7p&annotations=description,brand_summary,locations • schedules • http://atlas.metabroadcast.com/3.0/schedule.json?from=now&to=now.plus. 3h&channel=bbcone&publisher=bbc.co.uk • http://atlas.metabroadcast.com/3.0/schedule.json? from=1948-12-24&to=1948-12-25&channel=radio4&publisher=bbc.co.uk • api explorer http://atlas.metabroadcast.com/#apiExplorer
17. Why Cassandra? • scalability/performance • row caches • consistency control • column-based model matches our use case
18. And? • ElasticSearch • messaging • tooling: bootstraps
19. What is Atlas? BBC PA C4 etc... Data ingest server DB Update bus ES HTTP server
20. Data model • columns to model annotations • secondary indexes • index.direct(keyspace, SEGMENT_URI_INDEX_CF, ConsistencyLevel.CL_QUORUM). from(segment.getCanonicalUri()). to(segment.getIdentifier()). index().execute(requestTimeout, TimeUnit.MILLISECONDS);
21. ID generation • give external data our own ID on ingest • needs to be user-friendly: http://www.radiotimes.com/programme/cf2/eastenders • mongo: findAndModify() • solution: uses Astyanax client with its distributed locking • more details: http://metabroadcast.com/blog/let- cassandra-identify-your-data
22. Where we’re at • already live with some data • alpha release of schedule endpoint coming soon • later: roll out across other endpoints
23. Ops
24. Ops in Cassandra • we love Puppet • it’s great for automation and deployment • MongoDB: 1 file • Cassandra: 2 files! • oh... tokens
25. Cassandra Tokens • define where data is written to in a cluster • therefore balanced tokens = balanced cluster • tokens should be rack aware • tools available to provide appropriate tokens for you
26. Cassandra plays nicely with AWS • datacentre / rack aware • AWS Region = Datacentre • AWS Availability Zone = Rack • only recently introduced in MongoDB but simple to implement in Cassandra • horizontally (and vertically) scalable
27. Monitoring • Nagios is a little threadbare for Cassandra • basic TCP service check • stats from API not very helpful • nodetool and CLI tools useful • manual effort to integrate them • if only there was some useful service...
28. OpsCenter • wonderful for an overview • not so much for alerting ;) • ohai API • can integrate metrics into Nagios
29. Disaster Recovery • we operate a 4 node cluster presently • replication factor of 3 with quorum read/writes • DR complicated by tokens • cluster should be balanced • snapshot + S3 Backups
30. Cluster Happiness and Headaches • little maintenance overhead • cluster rebalancing • uncommon maintenance procedure • schema changes are cumbersome • little scope for rollback, can put cluster in unrecoverable state
31. Summary • Mongo is good, Atlas has outgrown it • Cassandra isn’t a drop-in replacement • Ops more complex but so far so good
32. Questions?