how to get results from different shards and same collection

0
votes

I created a test MongoDB Sharding with 1 Config Server, 1 Router and 2 Shards.

I created a config server with mongod --configsvr --dbpath /data/configdb --port 27019

And I run mongos with mongos --configdb <CONFIG SERVER IP>:27019. I connected shards and database and collections. When I query sharded collection, cursor doesn't get results from two shards, it gets results only 1 shard. According to MongoDB Sharding Document, I can distribute a collection to different shards but results didn't satisfy this information.

What am I doing wrong? What's the correct way to get results from different shards with same query?

1
mongodbsharding
This is really all about what you choose for a shard key and what your goals are. If you really "want" to scatter writes and reads across all shards then the shard key chosen should reflect that. For really even distribution then consider a hashed shard key. - Blakes Seven

1 Answers

1
votes

The correct way is to ensure that you do NOT have to go cross shard, often. You chose a shard key so that your queries for not end up going across shards. e.g. a user database could have user id/name as the shard key. Most queries go looking for a single user, so would come back from single shard.

For queries that cannot be satisfied with results from 1 shard alone, Mongo automatically requests data from all shards.