How to make data in a sharded collection move away from a shard [migrated] - mongodb

Question

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Migrated 3 days ago.
I have a sharded collection with 3 shards (shard1, shard2, shard3). Each shard is a 3-node replicaset (rs1, rs2, rs3).
I have a db called activity that has a large sharded collection called items. ie( activity.items). The data in this collection is split across shard{1,2,3}.
I have another db called app and collection called users (ie, app.users). This is not a sharded collection. It is housed on shard1.
I want the data from activity.items that current resides on shard1 to no longer reside on shard1. I don't want any activity.items data on shard1.. It should either move to shard2 or shard3. Or if it's easier, I can spin up a shard4
Is this possible? Any high level guidance on which commands to be looking at example docs would be greatly appreciated. I'm open to alternative solutions that achieve my goal of moving the activity.items collection data away from shard1.

Answer 1

You can use moveChunk command.
This old script is used to move everything to one shard (Primary), but you get the idea. In your case, use just filter (for source) only one shard and then for the destination you create "loop" where you distribute those chunks evenly to those other shards. Of course, you can move them to only one shard, and let the balancer to distribute those chunks.
database = 'activity'
collection = database + '.items.chunks'
sh.stopBalancer()
use config
primary = db.databases.findOne({_id: database}).primary
// move all chunks to primary
db.chunks.find({ns: collection, shard: {$ne: primary}}).forEach(function(chunk){
print('moving chunk from', chunk.shard, 'to', primary, '::', tojson(chunk.min), '-->', tojson(chunk.max));
sh.moveChunk(collection, chunk.min, primary);
});