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Querying data on a Mongodb Shard


Querying data on a Mongodb Shard

By : wakisi
Date : November 21 2020, 11:01 PM
I wish this help you Your application can't communicate directly with one shard and it is useless too. Maybe the following picture can help you to understand how sharding works in MongoDB.
The query router (also called mongos) works as a middleware: it receives a request from the client and directs it automatically to the correct(s) shard(s); when a shard is ready, sends its answer to this query router which shall forward it to the client. Using mongoDB sharding, the mongos instances use the metadata of your config servers to route a request just towards the affected shard(s). There is not any need to communicate directly with a shard, MongoDB does it for you.
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In 64-bit mongodb how AutomaticFailover works,when each shard has different data?

In 64-bit mongodb how AutomaticFailover works,when each shard has different data?


By : Vishal Mittal
Date : March 29 2020, 07:55 AM
I wish did fix the issue. Sharding is not about failover but rather about scalability. Failover achieved with replica sets. I.e. each shard is running as replica set with multiple nodes, when the master node fails new master node is elected among slave ones.
Here how it looks: http://www.infoq.com/resource/news/2010/08/MongoDB-1.6/en/resources/mongodb2.png
If a shard goes down, then, after re-allocating that shard, will data residing in that shard be retrievable

If a shard goes down, then, after re-allocating that shard, will data residing in that shard be retrievable


By : narendrasinhv
Date : March 29 2020, 07:55 AM
To fix the issue you can do Yes.
Once the node with primary shard number 2 goes down then the replica shard on the other node will be upgraded to a primary shard - allowing you to retrieve the data. See here:
Why when I add new collections just one shard gets the data? - MongoDB

Why when I add new collections just one shard gets the data? - MongoDB


By : Dimitris Soulios
Date : March 29 2020, 07:55 AM
To fix this issue MongoDB balance the shards by using the number of chunks, not documents (see https://docs.mongodb.com/manual/core/sharding-balancer-administration/). Therefore, from the output you provided, the cluster is balanced. Shard rs1 contains 36 chunks, and shard rs3 also contains 36 chunks for the pessoas collection.
If the number of documents is not balanced, that means that your inserts are going into a small number of chunks (or even a single chunk in the worst case), and not distributed across all the chunks. This typically caused by using a monotonically increasing shard key.
Querying data on a Mongodb Shard from the mongos

Querying data on a Mongodb Shard from the mongos


By : Bijay Pathak
Date : March 29 2020, 07:55 AM
With these it helps In practice, with a properly designed system, this is a situation that should never occur because every shard should consist of a replica set. When each shard is a replica set, you would have to have multiple failures for the shard to be down/unavailable.
If for some reason you do have a shard that is down some queries can still be performed. If the queries are targeted to only shards that are available, they will still work. But if your queries are broadcast queries, the query will fail.
Why do hashed shard keys create chunks on each shard in mongodb

Why do hashed shard keys create chunks on each shard in mongodb


By : Remy Nisbet
Date : March 29 2020, 07:55 AM
hope this fix your issue This is the actual behaviour of Hashed Sharding.
Shard an empty collection
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