sharding-notes.rst

Sharding Notes

Setting up a sharded cluster

Create directories for mongod instances:

mkdir /data/shard1 /data/shard2 /data/config

Start up 3 mongod instances:

mongod --dbpath /data/shard1 --port 10000 --shardsvr
mongod --dbpath /data/shard2 --port 10001 --shardsvr
mongod --dbpath /data/config --port 20000 --configsvr

Start an instance of mongos:

# --chunkSize 1 means use a 1MB chunk size. This is for
# demonstration purposes.
mongos --configdb localhost:20000 --chunkSize 1 --port 27100

Add shards to the cluster:

mongo --port 27100
mongos> use admin

# Pre MongoDB 2.0
mongos> db.runCommand({'addshard': 'localhost:10000'})
mongos> db.runCommand({'addshard': 'localhost:10001'})

# Post MongoDB 2.0
mongos> sh.addShard('localhost:10000')
mongos> sh.addShard('localhost:10001')

Enable sharding on a database:

# Pre MongoDB 2.0
mongos> db.runCommand({'enablesharding': <database name>})

# Post MongoDB 2.0
mongos> sh.enableSharding(<database name>)

Shard a collection:

# Pre MongoDB 2.0
mongos> db.runCommand({'shardcollection': <namespace>, 'key': <shard key>})

# Post MongoDB 2.0
mongos> sh.shardCollection(<namespace>, <shard key>)

Important Sharding Commands

sh.help()
db.printShardingStatus()

Exercises

1. Set up a sharded cluster on your local machine using the instructions above.
2. Generate some simple data using the example from the "General Ops Notes" page.
3. Shard the collection on a field (or fields) other than _id.
4. Explore the config db. Query the changelog and locks collections.