First of all, I'm a beginner in mongoDB so please be patient with me. I'm using windows and I created a simple database that contains 4 collections. When I'm dealing with mongoDB, I first run: mongod.exe --dbpath "Path To Data Folder" in a terminal and then I connect to the mongod using mongo.exe. What I'm supposed to do is to distribute the database along with its collections into shards and replica sets for supporting distributed queries.
I tried to use commands like sh.enableSharding("DATABASE NAME") but it didn't work. I then figured out that I need to run mongos instead of mongod, so I followed this: Sharding in MongoDB but unfortunately I didn't succeeded. I also did some research but it seems there is a lack of to-the-point guides on sharding and replication. So if you point me to the right direction, I would really appreciate it.
You can't enable sharding on a single database instance. You need to have at least 3 config server instances, two database (mongod) instances and a router instance (mongos). All of them should be running in the same time (i.e don't close the terminals in which you started all your instances).
A good starting point for you is to read the sharding tutorial in Deploy a Sharded Cluster - MongoDB.org
Related
Is there any ways or methods to start mongodb replication directly when mongod service start? I don't want to enter to shell and ON the replication?
Thanks!
You can create a mongod service which starts automatically when server starts.
First you need to create a configuration file(mongodb.conf) which will include configuration settings such as replicaSet name etc. Then create a service and install it using following command
mongod -f c:\mongod.conf --install
Then start the service using
net start mongodb
Read about configuration file here and
How to install mongo as service here
When you create a valid replica set in mongodb, your data will be asynchronously from the primary member to the secondary members in replica set
Having said that, you're not required to do extra efforts manually to get data replication done
When you do rs.slaveOk() on secondary, that allows you to query data from secondary members in the replica set.
It's a provision. It allows you to read from secondary provided that you're can tolerate the possible eventual consistent data. The replication does not happen when you do rs.slaveOk() on secondary
I'm not sure to understand. Your question was about service start. On my part, I install mongo on ubuntu and the service is not started with replicatet mode.
Finally, I disabled the first one and I created another service with the option --replSet myReplicat .
When you have only 2 servers, there is a problem with majority votes. On my part, I had 2 secondary after I stopped the primary and it was difficult to comeback with 1 primary and 1 secondary.
Effectively, the replication is always active. By default, all connections should go to the Primary. If you want to readonly from a secondary, you first enter the commande rs.slaveOk(). This command is active at session level. If you reconnect, you have to pass it again. It is not possible to put it at server side.
I am supposed to setup mongodb on 4 servers (a school project to benchmark mongodb, vs others). So I am thinking of using only sharding without replication. So I attempted to setup the 1st 3 server to run mongod --configsvr, and the 4th just a normal mongod instance. Then for all servers, I run mongos. Then I am at the part where I run sh.addShard("...") and I get
{
"ok" : 0,
"errmsg" : "the specified mongod is a --configsvr and should thus not be a shard server"
}
Seems like I cant have a config server running as a shard too? How then should I set things up?
No, the config server is not a shard. The config server is a special mongod instance that stores the sharded cluster metadata, essentially how the data is distributed across the sharded cluster.
You really only need 1 mongos instance for a simple setup like this. When you start mongos, you will provide it with the hostname(s) of your config server(s).
The Sharded Cluster Deployment Tutorial explains all of the steps that you need to follow.
For development reasons, I need to backup a production replica set mongodb and restore it on a stand alone, different machine test instance.
Some docs are talking about the opposite ( standalone 2 replica-set ), but I cannot find his downgrade/rollback way.
What's the way to go, in this case ?
No matter how many nodes you have in a replica set, each of them holds the same data.
So getting the data is easy - just use mongodump (preferably against the secondary, for performance reasons) and then mongorestore into a new mongod for your development stand-alone system.
mongodump does not pick up any replication related collections (they live in database called local). If you end up taking a file system snapshot of a replica node rather than using mongodump, be sure to drop the local database when you restore the snapshot into your production stand-alone server and then restart mongod so that it will properly detect that it is not part of a replica set.
What is the easiest way to setup a sharded cluster with MongoDB?
Start the mongo shell without connecting to a database:
mongo --nodb
Then start a new sharding test specifying the number of mongos and shards that you would like:
new ShardingTest({ shards: 2, mongos: 1 })
The logging output from each of the processes will be piped to this single shell (so there will be a lot). This makes that shell somewhat unusable but at least it only takes up one window and spares you from having to fork and specify a log path.
Just open up another shell and you are ready to go. Connect to the first mongos on port 30999.
we are going to use mongo db for an alert monitoring application.
We thought first to write the data to files and then to write it onto mongodb using mongoimport utility. Each file will have 1Mill records on an average.
Here my question is "shall we sharding here...?"
I guess mongoimport is not aware of sharding.
How does sharding works when writes are happening by mongoimport...?
If your collection exists and is sharded and you run mongoimport against a mongos router, then it will respect sharding rules (writes will be distributed according to chunk location).
Footnote
If you have a mongodb cluster, you have to have mongos daemon(s) in there. mongos reads your cluster configuration from config servers and knows where to route requests from your app. In a cluster configuration you should never talk to mongod servers directly, only via mongos. Read more about cluster configuration here.