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2011 mongo sf-sharding


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2011 mongo sf-sharding

  1. 1. The Secret Sauce of Sharding Eliot Horowitz @eliothorowitz MongoSF May 24 2011
  2. 2. Architecture Shards mongod mongod mongod ... mongod mongod mongod mongod mongod mongod Config Serversmongod mongos mongos ...mongodmongod client client client client
  3. 3. Common Setup• A common setup is 3 shards with 3 servers per shard: 3 masters, 6 slaves• Can add sharding later to an existing replica set with no down time• Can have sharded and non-sharded collections
  4. 4. Range Based MIN MAX LOCATION A F shard1 F M shard1 M R shard2 R Z shard3• collection is broken into chunks by range• chunks default to 64mb or 100,000 objects
  5. 5. Config Servers• 3 of them• changes are made with 2 phase commit• if any are down, meta data goes read only• system is online as long as 1/3 is up
  6. 6. mongos• Sharding Router• Acts just like a mongod to clients• Can have 1 or as many as you want• Can run on appserver so no extra network traffic• Cache meta data from config servers
  7. 7. Writes• Inserts : require shard key, routed• Removes: routed and/or scattered• Updates: routed or scattered
  8. 8. Queries• By shard key: routed• sorted by shard key: routed in order• by non shard key: scatter gather• sorted by non shard key: distributed merge sort
  9. 9. Splitting• Take a chunk and split it in 2• Splits on the median value• Splits only change meta data, no data change
  10. 10. SplittingT1 MIN MAX LOCATION A Z shard1T2 MIN MAX LOCATION A G shard1 G Z shard1T3 MIN MAX LOCATION A D shard1 D G shard1 G S shard1 S Z shard1
  11. 11. Balancing• Moves chunks from one shard to another• Done online while system is running• Balancing runs in the background
  12. 12. MigratingT3 MIN MAX LOCATION A D shard1 D G shard1 G S shard1 S Z shard1T4 MIN MAX LOCATION A D shard1 D G shard1 G S shard1 S Z shard2T5 MIN MAX LOCATION A D shard1 D G shard1 G S shard2 S Z shard2
  13. 13. Setting it Up• Start servers• add shards: db.runCommand( { addshard : "" } )• turn on partitioning: db.runCommand( { enablesharding : "test" }• shard a collection: db.runCommand( { shardcollection : "" , key : { num : 1 } } )
  14. 14. Live Migration• Copy initial data set• Copy anything modified since start• Commit start• Copy delta• Finish commit
  15. 15. Download MongoDB and
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