I build a MongoDB sharding environment and want to test the performance of migration data.
I insert one billion rows in a collection in Replica Set A.
I added another shard setting Replica Set B.
MongoDB starts to balance chunks between those shards.
After balancing is finished, I found out I can't look up some data.
Because those data have been moved to Replica Set B, only when I restart all mongo router service am I able to query them.
Is it a normal and inevitable procedure, or is there any way to reload the whole system (through mongo shell command or anything else)?
Thank you !!!
I found a command that it seems help to reload the router config
db.adminCommand({"flushRouterConfig":1});
2017-05-18 After testing, it works!
Related
I am new to mongoDB while going through some tutorial I got a question in my mind that, in sharded environment during reading operation "mongos" first checks config server to get details to which shard it has to query. But what about during write operation does it first checks to which shard it has to perform write operation?
Thanks in advance,
Kitty
I am going to answer based on the current stable release of MongoDB v3.2.
The config servers store the cluster's metadata in the config database. The mongos instances cache this data and use it to route reads and writes to shards.
MongoDB only writes data to the config servers when the metadata changes, such as:
After a chunk migration, or
After a chunk split.
MongoDB reads data from the config server in the following cases:
A new mongos starts for the first time, or an existing mongos restarts.
After change in the cluster metadata, such as after a chunk migration.
See also: Sharded Cluster Mechanics.
Can we have this type of configuration?
Two server running the following things each-
1.Mongo Config Server.
2.Mongo Router.
3.Application.
Total 4 EC2 servers-
First Server-Running the web application & mongos.
Second Server-Running the web application & mongos.
Third Server-Running the First Shard with complete DB(Say for
example Demo).
Forth Server-Running The Second Shard with complete DB(Say for
example Demo).
Both the Mongos should point to one shard named Shard1?
Yes, You can have multiple mongos instances running against a single shard. Think of the mongos instances as clients for the sharded cluster which have to run as a daemon process in order to keep metadata and heartbeats up to date.
Edit: as for having a complete DB, this is only possible for a single DB. You can have one DB on shard1 and the other DB on shard2, for example. but you can never have a single complete DB on two shards. To achieve the goal of having db1 on shard1 and db2 on shard2, you simply make the respective shard the primary shard of the respective database and don't shard any collection. Please read the docs for the movePrimary command for details.
A bit OOT:
However, running a single config server is strongly advised against, and for a good reason. If the single config server goes down or gets corrupted, your cluster will be impossible to use - and recreating the sharded cluster will not an easy task to be done. And it's going to be a lengty process. So please, use three config servers.*
I have a sharded cluster which is set up , Since my data is seamlessly growing , I need to keep monitoring the size of data and add new shards to the cluster .
Is there a command that I could use to know how much size is utilized in each sharded server , at any point of time .
For eg . lets say I have a database , and my show dbs command from mongos console shows like this
mongos> show dbs
company 0.375GB
config 0.046875GB
test 0.0625GB
I want to know how much data is used in each shard servers . for company database .
my implemented architecture is as follows
I have a single database sharded , in which each collection is sharded .
3 shard servers running mongod instances
1 server running mongos
1 server running config instance
My whole application layer is talking to mongos directly .
I need to know this because , I am planning to build a cron which checks the available size of the shard server and if it exceeds some amount it will send a notification to administrator to show some attention .
Thanks in advance for responding to this post
After posting in the mongoDB user group , I got the solution on how we need to do this and what commands that could be used
Commands
To know about space utilization of a particular DB in each sharded server we have to use
db.stats()
to know about space utilization of a particular Collection in each sharded server we have to use
db.<collectionname>.stats()
Now to use it in the php daemon/cron I could call these commands using php mongo driver
$con= new Mongo()
$stats=$con->dbName->command(array('dbStats' => 1)); // for db.stats()
$stats=$con->dbName->command(array('collStats' => 'collection_name'));
Still I couldn't find any method to execute such commands from Zend shanty mongo but I could use default PHP pecl mongo db driver to achieve this
Thank you all for responding to this post
There are general monitoring solutions for that (nagios, zabbix, etc). They monitor many parameters of your machines and can be set up to send alerts in certain situations. You don't need to reinvent the wheel.
Such general solution can also warn you if you're running out of space on an app server (because its logs take all the space). Your specialized mongodb cron job won't be able to do that.
I am using 64-bit MongoDB, and i am undergoing test on multiple-shards. If i keep multiple shards in a single machine. Its working fine but if i keep shards in different machine, its failed in sharding to second shard. I have restricted the first-shard size to 10MB, once its reaches the limited size in first shard it should start sharding to second-shard but not happening so.Instead failed to store in second-shard updating to first shard. The following are my shard details. In my environment initially i have two shards. The first shard is on my first-machine running along with my application. The Second-shard is on my second machine.
Configuration as follows:-
*)On both of my shards, shard-server,configserver,mongos and i have connected mongo through mongos as follows ./mongo hostname:27017/admin and i have added both the shards in first & second shard and enabled sharding for database and collection level by using shard-key.
Please, let me know if i gone wrong anywhere in the configuration.
Advance Thanks,
Your post could use some editing, this is very difficult to read.
It looks like you have 2 machines. On each machine you have:
mongod process serving as one shard
mongod process serving as a config
mongos process
a copy of your application connecting to localhost:27017/admin
Please, let me know if i gone wrong anywhere in the configuration.
There are several possible problems here. Please check the following:
You can only have 1 or 3 config processes. It looks like you have 2, this will not work.
When you connect to localhost:27017/admin are you connecting to mongos or mongod? Either one could be running on those ports. Can you specify the ports for each process to help clarify? You must connect to mongos or the sharding will not happen.
Please look at the logs, they generally have output indicating what the server is doing. If there is no indication of "splits" or "chunks" happening, then your database may be configured incorrectly.
Your best bet is to start from top and test each piece one at a time.
I've a working MongoDB "replica set" made up by 3 servers.
It is storing two DBs, I wonder if is it possible to replicate only one of the DBs without running more than one mongoDB instance(one per DB).
Here is a sketch of the "problem"
Server1 Server2 Server3
DB1 X X X
DB2 X X
X stands for Server where DBs have to be replicated in.
thank
I don't believe it is possible.
Unlike sharding, where you specify down to the collection level what gets sharded, with replica sets you're defining that a given MongoDB instance is part of a replica set. As only one node in a replica set can be the master at any given time, based on the scenario you are talking about, then there would be a problem if e.g. Server1 went down and Server3 was promoted to master - as DB2 would then not be able to be written to.
I had a simliar problem and found a quite easy solution in javascript to be executed in a mongo-shell.
Sourcecode available here:
http://www.suenkel.de/blog/2012/02/mongodb-replicate-one-database-or-collection/
With opening a tailable cursor on the oplog of the master server each operation could be applied to another server (of course you can filter by the namespace of the collections or even the databases...)
According to current MongoDB ReplicaSet architecture, you can't use a single Replica Set with some members having parts of the databases or collections.
However, if you have the requirement of replicating a single database or collection in real-time in another location, I ended up with following workaround:
Use directoryPerDB to separate the desired database files (Create a new replica with this option enabled if you don't have this already)
Copy the directory of desired database to the new location.
Deploy a new ReplicaSet with this single database.
Write a simple script and use Change Streams to perform the replication for you.
As I said, you will end up with another Replica Set dedicated for this database, but replication is done in real-time and both Replica Sets has the data in a consistent way (You have to perform your write operations on first ReplicaSet, though).