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Vinodh Krishnaswamy

MongoDB Sharded Cluster - How to design your topology

Support Engineer - MongoDB & MySQL Percona

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◆ Started as MySQL DB DBA

◆ Support for MongoDB

◆ Trainer

◆ Scripting, Reading, Driving

◆ “Guruji” - who shares knowledge◆ Now here I am - Perconian!!!

Who am I

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Agenda▪ Sharded Cluster - components

▪ Ranged Sharding

▪ Hashed Sharding

▪ Zones / Tags

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Agenda

▪ HA

▪ ReplicaSet - Key points

▪ Topology

▪ Q&A

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Sharded Cluster

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Sharded Cluster▪ Horizontal Scaling

•Data across multiple nodes

• Reduce stress for larger working set

• Ability to add more servers

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Architecture

mongos

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Sharded Cluster

▪ Shard Key

▪ Chunks

▪ Balancer - Chunk distribution

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POINTS TO NOTE

TARGET vs BROADCAST

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Primary Shard

A

A

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Primary Shardsh.status()

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Primary Shard▪ Routing - sharded vs unsharded

▪ Keep at right shard

db.adminCommand( { movePrimary:

<databaseName>, to: <newPrimaryShard> } )

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Ranged Sharding

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Strategy

▪ Ranged Sharding

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Strategy

▪ Ranged Sharding

sh.shardCollection( "database.collection", { <shard

key> } )

Example:

sh.shardCollection( "vinodh.testData", { empNo: 1 } )

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Monotonically Changing Shard Key

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Ranged Sharding▪ Contiguous ranges determined by Shard Key

▪ Default method

▪ Efficient when

• High cardinality

• Low Shard Key frequency

• Non-Monotonically Changing Shard key

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Hashed Sharding

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Strategy

▪ Hashed Sharding

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Strategy▪ Hashed Sharding uses hashed index

sh.shardCollection( "database.collection", {

<field> : “hashed” } )

Example:

sh.shardCollection( "vinodh.testData",

{ UUIDfield: “hashed” } )

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Monotonically Changing Shard Key - Hash

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Hashed Sharding▪ Provides equal distribution

▪ Target vs Broadcast operations

▪ Ideal for fields that changes monotonically like

ObjectID, timestamp etc

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Zones

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Why Zones?

▪ Isolate data set

▪ Geographically closest

▪ Route data to desired Shard h/w

▪ Distribute Writes based on DC

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How to...▪ First create tagRange with Shards

sh.addShardTag("shard01", "tag1")

sh.addShardTag("shard02", "tag2")

▪ Assign tagRanges to collections

sh.addTagRange( "<database>.<collection>",

{ "gender" : "Male", "userid" : MinKey },

{ "gender" : "Male", "userid" : MaxKey },

"tag1")

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Zone

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Zone

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HA overview

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HA

• Instance down

• Loss of DC

•Network Partition

•Backup

•Etc.

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HA

▪ Sharded Cluster itself is NOT HA

▪ SC + RS = Complete HA

▪ Failover Scenarios - Do your Exercise!

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ReplicaSet - Key Points

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Replicaset

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Replicaset

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Replicaset - ARBITER

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replicaSet Configuration

▪ Priority

▪ Hidden

▪ Delayed

▪ Arbiter

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Replicaset - Election+Priority

ELECTION - VOTING & CHOOSING

Priority: 5Priority: 1

Priority: 1 Priority: 5

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Points to Note

▪ Set proper {Priority:n} to elect a member as

Primary

•Avoid setting Priority for all members

▪ Set {writeConcern:majority} to avoid data loss

▪ Set readPreference for reads

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Topology- Application Servers

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Applications and mongos in one server

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mongos/router in each Application servers

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Sharded Cluster in Private network

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Topology- Shards

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Shard instances deployed in dedicated servers design

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Multiple Shard members in each Server + HA design

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Production DC and DR DC + HA design

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Using Zones / Tags + HA design

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Points to Note

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POINTS TO NOTE▪ SHARD KEY - Pain Point!

•Monotonically increased key

•Do your tests!

▪ SHARD EARLY!

▪ ZONES

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POINTS TO NOTE

BACKUP + RESTORE

https://www.percona.com/blog/2018/12/13/mongodb-backup-how-and-when-to-use-psmdb-hotbackup-and-mongodb_consistent_backup/

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Question?vinodh.krishnaswamy@percona.comhttps://in.linkedin.com/in/vinodhkrish

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THANK YOU