M103 mongod mongos Options

 

 

 

chmod 400 <path-to-the-file>

chmod 400 /var/mongodb/pki/m103-keyfile

chown [new owner]:[group] <file name>

sudo chown myuser:myuser /var/mongodb_directory

mkdir [modifiers] <name of the directory>

mkdir -p /db/mongodb_data/

sudo mkdir -p /var/data

rm [options] [directory|file]

rm -rf <directory name>

ls

ls -la

cd <directory>

cat <name of the file>

 

 

rm <file name>

ps -ef | grep mongo

ps -ef | grep mongod

ps -ef | grep mongos

 

 

kill <pid>

kill 13029

killall mongod

 

 

https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard

Filesystem Hierarchy Standard - Wikipedia

 

 

 

 

 

mongod

mongo

db.createCollection("employees")

use admin

db.shutdownServer()

exit

 

 

Which of these are default configurations for mongod?

- mongod listens on port 27017

- database files are stored in the directory /data/db/

 

mongod --help

mongod --dbpath <directory path>

mongod --port <port number>

mongod --auth

mongod --bind_ip 123.123.123.123

mongod --bind_ip localhost,123.123.123.123

 

https://www.mongodb.com/docs/manual/reference/program/mongod/#bin.mongod

mongod — MongoDB Manual

 

mongod

 

mongod --dbpath /data/db --logpath /data/log/mongod.log

 

mongod --dbpath /data/db --logpath /data/log/mongod.log --fork

 

mongod --dbpath /data/db --logpath /data/log/mongod.log --fork --replSet "M103" --keyFile /data/keyfile --bind_ip "127.0.0.1,192.168.103.100" --tlsMode requireTLS --tlsCAFile "/etc/tls/TLSCA.pem" --tlsCertificateKeyFile "/etc/tls/tls.pem"

 

storage: dbPath: "/data/db" systemLog: path: "/data/log/mongod.log" destination: "file" replication: replSetName: M103 net: bindIp : "127.0.0.1,192.168.103.100" tls: mode: "requireTLS" certificateKeyFile: "/etc/tls/tls.pem" CAFile: "/etc/tls/TLSCA.pem" security: keyFile: "/data/keyfile" processManagement: fork: true

 

 

https://www.mongodb.com/docs/manual/reference/program/mongod/#options

mongod — MongoDB Manual

 

https://www.mongodb.com/docs/manual/reference/configuration-options/

Configuration File Options — MongoDB Manual

 

 

mongod --dbpath /data/db --logpath /data/logs --replSet M103 --bind_ip '127.0.0.1,192.168.103.100' --keyFile /data/keyfile --fork

Which of the following represents a configuration file equivalent to the command line options?

 

storage:
  dbPath: "/data/db"
systemLog:
  destination: file
  path: "/data/logs"
replication:
  replSetName: "M103"
net:
  bindIp: "127.0.0.1,192.168.103.100"
security:
  keyFile: "/data/keyfile"
processManagement:
  fork: true

 

 

mongod --config mongod.conf

mongod -f mongod.conf

 

mongo admin --host localhost:27000 --eval '

  db.createUser({

     user: "m103-admin",

     pwd: "m103-pass",

     roles: [

        {role: "root", db: "admin"}

     ]

   })

'

 

 

https://www.mongodb.com/docs/manual/reference/configuration-options/#storage.journal.commitIntervalMs

Configuration File Options — MongoDB Manual

 

 

ls -l /data/db

 

ls -l /data/db/diagnostic.data

 

ls -l /data/db/journal

 

ls /tmp/mongodb-27017.sock

 

Which of the following files in the MongoDB data directory can you access to view collection data?

- The correct answer is none of the above. You should never access the data files directly.

 

 

 

mkdir -p /var/mongodb/db

 

mongo admin --host localhost:27000 --eval '

 db.createUser({

  user: "m103-admin",

  pwd: "m103-pass",

 roles: [

  {role: "root", db: "admin"}

 ]

})

'

mongod --config mongod.conf --dbpath /var/mongodb/db --port 27000

 

 

https://www.mongodb.com/docs/manual/reference/explain-results/#explain.queryPlanner.optimizedPipeline

Explain Results — MongoDB Manual

 

 

db.createUser()

db.dropUser()

 

db.<collection>.renameCollection()

db.<collection>.createIndex()

db.<collection>.drop()

 

db.dropDatabase()

db.createCollection()

 

db.serverStatus()

 

db.runCommand({

 "createIndexes":"<collection_name>",

 "indexes":[

   {

    "key":{ "product": 1 },

    "name": "name_index"

   }

  ]

 }

)

 

 

db.<collection>.createIndex(

  { "product": 1 },

  { "name": "name_index" }

)

 

db.<collection>.createIndex

 

Which of the following methods executes a database command?

- db.runCommand( { <COMMAND> } )

 

 

https://www.mongodb.com/docs/manual/release-notes/4.2/#logging-and-diagnostics

Release Notes for MongoDB 4.2 — MongoDB Manual

 

 

 

 

mongo admin --host 192.168.103.100:27000 -u m103-admin -p m103-pass --eval ' db.getLogComponents() '

 

mongo admin --host 192.168.103.100:27000 -u m103-admin -p m103-pass --eval ' db.setLogLevel(0, "index") '

 

db.adminCommand({ "getLog": "global" })

 

tail -f /data/db/mongod.log

 

mongo admin --host 192.168.103.100:27000 -u m103-admin -p m103-pass --eval ' db.products.update( { "sku" : 6902667 }, { $set : { "salePrice" : 39.99} } ) '

 

grep -i 'update' /data/db/mongod.log

 

 

Which of the following operations can be used to access the logs?
- Running db.adminCommand({ "getLog": "global" }) from the Mongo shell
- Running tail -f <path-to-log-file> from the command line

 

 

 

db.runCommand({listCollections: 1})

 

mongo newDB --host 192.168.103.100:27000 -u m103-admin -p m103-pass --authenticationDatabase admin --eval ' db.getProfilingLevel() '

 

mongo newDB --host 192.168.103.100:27000 -u m103-admin -p m103-pass --authenticationDatabase admin --eval ' db.setProfilingLevel(1) '

 

mongo newDB --host 192.168.103.100:27000 -u m103-admin -p m103-pass --authenticationDatabase admin --eval ' db.getCollectionNames() '

 

mongo newDB --host 192.168.103.100:27000 -u m103-admin -p m103-pass --authenticationDatabase admin --eval ' db.setProfilingLevel( 1, { slowms: 0 } ) '

 

mongo newDB --host 192.168.103.100:27000 -u m103-admin -p m103-pass --authenticationDatabase admin --eval ' db.new_collection.insert( { "a": 1 } ) '

 

mongo newDB --host 192.168.103.100:27000 -u m103-admin -p m103-pass --authenticationDatabase admin --eval ' db.system.profile.find().pretty() '

 

Which of the following events are captured by the profiler?

- Administrative operations

- CRUD operations

- Configuration operations

 

mongod --config mongod.conf --dbpath /var/mongodb/db --port 27000 --logpath /var/mongodb/logs/mongod.log --fork

 

mongod -f mongod.conf --port 27000 --auth

 

 cat /etc/mongod.conf

 mongod -f /etc/mongod.conf

mongo --host 127.0.0.1:27017

use admin
db.createUser({
  user: "root",
  pwd: "root123",
  roles : [ "root" ]
})

mongo --username root --password root123 --authenticationDatabase admin

db.stats()

use admin
db.shutdownServer()



When should you deploy a MongoDB deployment with security enabled?
- When deploying a development environment
- When deploying your staging environment
- When deploying an evaluation environment
- When deploying your production environment

 

 

https://university.mongodb.com/courses/M310/about

Free MongoDB Official Courses | MongoDB University

 

 

 

mongo admin -u root -p root123

db.createUser(
  { user: "security_officer",
    pwd: "h3ll0th3r3",
    roles: [ { db: "admin", role: "userAdmin" } ]
  }
)

db.createUser(
  { user: "dba",
    pwd: "c1lynd3rs",
    roles: [ { db: "admin", role: "dbAdmin" } ]
  }
)

db.grantRolesToUser( "dba",  [ { db: "playground", role: "dbOwner"  } ] )

db.runCommand( { rolesInfo: { role: "dbOwner", db: "playground" }, showPrivileges: true} )

 

 

Which of the following actions are granted to the userAdmin built-in role?
- dropRole
- createRole
- viewUser

Which of the following are true about replication in MongoDB?

- In the event of failover, the nodes vote to elect a new primary.

- The secondary nodes replicate data from the primary node.

 

 

http://thesecretlivesofdata.com/raft/

Raft

 

https://raft.github.io/

Raft Consensus Algorithm

 

replica sets in MongoDB?

- Replica set members have a fixed role assigned.

- We should always use arbiters.

- We can have up to 50 voting members in a replica set.

 

 

storage:
  dbPath: /var/mongodb/db/node1
net:
  bindIp: 192.168.103.100,localhost
  port: 27011
security:
  authorization: enabled
  keyFile: /var/mongodb/pki/m103-keyfile
systemLog:
  destination: file
  path: /var/mongodb/db/node1/mongod.log
  logAppend: true
processManagement:
  fork: true
replication:
  replSetName: m103-example

sudo mkdir -p /var/mongodb/pki/
sudo chown vagrant:vagrant /var/mongodb/pki/
openssl rand -base64 741 > /var/mongodb/pki/m103-keyfile
chmod 400 /var/mongodb/pki/m103-keyfile

 

mkdir -p /var/mongodb/db/node1

 

mongod -f node1.conf

 

cp node1.conf node2.conf
cp node2.conf node3.conf

 

vi node2.conf

 

:wq

 

storage:
  dbPath: /var/mongodb/db/node2
net:
  bindIp: 192.168.103.100,localhost
  port: 27012
security:
  keyFile: /var/mongodb/pki/m103-keyfile
systemLog:
  destination: file
  path: /var/mongodb/db/node2/mongod.log
  logAppend: true
processManagement:
  fork: true
replication:
  replSetName: m103-example

 

storage:
  dbPath: /var/mongodb/db/node3
net:
  bindIp: 192.168.103.100,localhost
  port: 27013
security:
  keyFile: /var/mongodb/pki/m103-keyfile
systemLog:
  destination: file
  path: /var/mongodb/db/node3/mongod.log
  logAppend: true
processManagement:
  fork: true
replication:
  replSetName: m103-example

 

mkdir /var/mongodb/db/{node2,node3}

 

mongod -f node2.conf
mongod -f node3.conf

 

mongo --port 27011

 

rs.initiate()

 

use admin
db.createUser({
  user: "m103-admin",
  pwd: "m103-pass",
  roles: [
    {role: "root", db: "admin"}
  ]
})

 

exit
mongo --host "m103-example/192.168.103.100:27011" -u "m103-admin"
-p "m103-pass" --authenticationDatabase "admin"

 

rs.status()

 

rs.add("m103:27012")
rs.add("m103:27013")

 

rs.isMaster()

 

rs.stepDown()

 

rs.isMaster()

 

 

about setting up a replica set

- rs.initiate() must be run on every node in the replica set.

- Enabling internal authentication in a replica set implicitly enables client authentication.

 

 

Chapter 2: Replication

Lab: Deploy a Replica Set

 

mongod --replSet m103-repl --dbpath /var/mongodb/db/1 --keyFile /var/mongodb/pki/m103-keyfile --port 27001 --auth
mongod --replSet m103-repl --dbpath /var/mongodb/db/2 --keyFile /var/mongodb/pki/m103-keyfile --port 27002 --auth
mongod --replSet m103-repl --dbpath /var/mongodb/db/3 --keyFile /var/mongodb/pki/m103-keyfile --port 27003 --auth

 

rs.initiate()

 

db.createUser({ user: "m103-admin", pwd: "m103-pass", roles: [ {role: "root", db: "admin"} ] })

 

mongo admin -u m103-admin -p m103-pass --port 27001

 

use admin

rs.add("localhost:27002")

rs.add("localhost:27003")

 

12 total, 12 passed, 0 skipped:
[PASS] "localhost:27001 is running"
[PASS] "localhost:27002 is running"
[PASS] "localhost:27003 is running"
[PASS] "Replication is enabled on localhost:27001"
[PASS] "Replication is enabled on localhost:27002"
[PASS] "Replication is enabled on localhost:27003"
[PASS] "Replica set 'm103-repl' has the correct name"
[PASS] "The replica set 'm103-repl' contains localhost:27001"
[PASS] "The replica set 'm103-repl' contains localhost:27002"
[PASS] "The replica set 'm103-repl' contains localhost:27003"
[PASS] "The replica set enforces client authentication"
[PASS] "The replica set m103-repl uses keyfile authentication"

 

Which of the following fields are included in the replica set configuration document?

- version

- members

- _id

 

 

 

rs.status()

 

rs.isMaster()

 

db.serverStatus()['repl']

 

rs.printReplicationInfo()

 

 

What information can be obtained from running rs.printReplicationInfo()?

- The time of the latest entry in the oplog.

- The time of the earliest entry in the oplog.

 

mkdir allbymyselfdb
mongod --dbpath allbymyselfdb

mongo
show dbs

use local
show collections

use local
db.oplog.rs.find()

var stats = db.oplog.rs.stats()

stats.capped

stats.size

stats.maxSize

rs.printReplicationInfo()

 

 

 

Chapter 2: Replication

Local DB: Part 2

use m103 db.createCollection('messages')

 

use local
db.oplog.rs.find( { "o.msg": { $ne: "periodic noop" } } ).sort( { $natural: -1 } ).limit(1).pretty()

use m103
for ( i=0; i< 100; i++) { db.messages.insert( { 'msg': 'not yet', _id: i } ) }
db.messages.count()

use local
db.oplog.rs.find({"ns": "m103.messages"}).sort({$natural: -1})

use m103
db.messages.updateMany( {}, { $set: { author: 'norberto' } } )
use local
db.oplog.rs.find( { "ns": "m103.messages" } ).sort( { $natural: -1 } )

 

 

- The oplog.rs collection contains all operations that will be replicated.

- The local database will not be replicated.

 

 

 

Chapter 2: Replication

Reconfiguring a Running Replica Set

node4.conf

storage:
  dbPath: /var/mongodb/db/node4
net:
  bindIp: 192.168.103.100,localhost
  port: 27014
systemLog:
  destination: file
  path: /var/mongodb/db/node4/mongod.log
  logAppend: true
processManagement:
  fork: true
replication:
  replSetName: m103-example


arbiter.conf

storage:
  dbPath: /var/mongodb/db/arbiter
net:
  bindIp: 192.168.103.100,localhost
  port: 28000
systemLog:
  destination: file
  path: /var/mongodb/db/arbiter/mongod.log
  logAppend: true
processManagement:
  fork: true
replication:
  replSetName: m103-example


mongod -f node4.conf
mongod -f arbiter.conf


rs.add("m103:27014")
rs.addArb("m103:28000")

rs.isMaster()

rs.remove("m103:28000")

cfg = rs.conf()

cfg.members[3].votes = 0
cfg.members[3].hidden = true
cfg.members[3].priority = 0

rs.reconfig(cfg)

about reconfiguring a replica set with rs.reconfig()?
- It does not require any of the nodes to restarted.
- It does not require any of the configuration files to be updated.



mongo admin -u m103-admin -p m103-pass --port 27001


cfg = rs.conf()

cfg.members[3].votes = 0
cfg.members[3].hidden = true
cfg.members[3].priority = 0

rs.reconfig(cfg)


3 total, 3 passed, 0 skipped:
[PASS] "localhost:27004 has zero (0) votes"
[PASS] "localhost:27004 is hidden"
[PASS] "localhost:27004 has priority zero (0)"



Chapter 2: Replication

Reads and Writes on a Replica Set

mongo --host "m103-example/m103:27011" -u "m103-admin" -p
"m103-pass" --authenticationDatabase "admin"

rs.isMaster()

use newDB
db.new_collection.insert( { "student": "Matt Javaly", "grade": "A+" } )

mongo --host "m103:27012" -u "m103-admin" -p "m103-pass"
--authenticationDatabase "admin"

show dbs

rs.slaveOk()

use newDB
db.new_collection.find()

db.new_collection.insert( { "student": "Norberto Leite", "grade": "B+" } )

use admin
db.shutdownServer()

mongo --host "m103:27011" -u "m103-admin" -p "m103-pass"
--authenticationDatabase "admin"

rs.isMaster()

 

 about reading and writing from secondaries?
- We have to run rs.slaveOk() before we can read from secondary nodes.

 

 

Chapter 2: Replication

Failover and Elections

cfg = rs.conf()

 

cfg.members[2].priority = 0

 

rs.reconfig(cfg)

 

rs.isMaster()

 

rs.stepDown()

 

rs.isMaster()

 

 

Which of the following is true about elections?

- Nodes with priority 0 cannot be elected primary.

- Nodes with higher priority are more likely to be elected primary.

 

 

 

Chapter 2: Replication

Write Concerns: Part 1

Write Concerns: Part 2

 

Consider a 3-member replica set, where one secondary is offline. Which of the following write concern levels can still return successfully?

- majority

 

 

 

 

Chapter 2: Replication

Lab - Writes with Failovers

 

 

Problem:

Evaluate the effect of using a write concern with a replica set where one node has failed.

Consider a 3-node replica set with only 2 healthy nodes, that receives the following insert() operation:

 

use payroll
db.employees.insert(
  { "name": "Aditya", "salary_USD": 50000 },
  { "writeConcern": { "w": 3, "wtimeout": 1000 } }
)

Which of the following is true about this write operation?

- The unhealthy node will receive the new document when it is brought back online.

- If a writeConcernError occurs, the document is still written to the healthy nodes.

 

 

 

Chapter 2: Replication

Read Concerns

Which of the following read concerns only return data from write operations that have been committed to a majority of nodes?

- linearizable

- majority

 

 

 

Chapter 2: Replication

Read Preferences

Which of the following read preference options may result in stale data?

- secondary
- nearest
- primaryPreferred
- secondaryPreferred

 

 

Chapter 2: Replication

Lab: Read Preferences

 

Consider a 3-node replica set that experiences a network outage.

Two of the three nodes were unreachable during the outage, leaving one node remaining.

Which of these readPreferences will allow you to read data from this node?

 

- primaryPreferred

- secondaryPreferred

- nearest

- secondary

 

 

 

Chapter 3: Sharding

When to Shard

We should consider sharding when:

- we are holding more than 5TB per server and operational costs increase dramatically.

- government regulations require data to be located in a specific geography.

- our organization outgrows the most powerful servers available, limiting our vertical scaling options.

 

 

Chapter 3: Sharding

Sharding Architecture

In a sharded cluster, collection metadata is stored in:

- the configuration servers.

 

 

 

Chapter 3: Sharding

Setting Up a Sharded Cluster

 

Configuration file for first config server 

 

csrs_1.conf

sharding:
  clusterRole: configsvr
replication:
  replSetName: m103-csrs
security:
  keyFile: /var/mongodb/pki/m103-keyfile
net:
  bindIp: localhost,192.168.103.100
  port: 26001
systemLog:
  destination: file
  path: /var/mongodb/db/csrs1.log
  logAppend: true
processManagement:
  fork: true
storage:
  dbPath: /var/mongodb/db/csrs1

 

 

csrs_2.conf

sharding:
  clusterRole: configsvr
replication:
  replSetName: m103-csrs
security:
  keyFile: /var/mongodb/pki/m103-keyfile
net:
  bindIp: localhost,192.168.103.100
  port: 26002
systemLog:
  destination: file
  path: /var/mongodb/db/csrs2.log
  logAppend: true
processManagement:
  fork: true
storage:
  dbPath: /var/mongodb/db/csrs2

 

csrs_3.conf

sharding:
  clusterRole: configsvr
replication:
  replSetName: m103-csrs
security:
  keyFile: /var/mongodb/pki/m103-keyfile
net:
  bindIp: localhost,192.168.103.100
  port: 26003
systemLog:
  destination: file
  path: /var/mongodb/db/csrs3.log
  logAppend: true
processManagement:
  fork: true
storage:
  dbPath: /var/mongodb/db/csrs3

 

Starting the three config servers:

mongod -f csrs_1.conf
mongod -f csrs_2.conf
mongod -f csrs_3.conf

 

Connect to one of the config servers:

mongo --port 26001

 

Initiating the CSRS:

rs.initiate()

 

Creating super user on CSRS:

use admin
db.createUser({
  user: "m103-admin",
  pwd: "m103-pass",
  roles: [
    {role: "root", db: "admin"}
  ]
})

 

Authenticating as the super user:

db.auth("m103-admin", "m103-pass")

 

Add the second and third node to the CSRS:

rs.add("192.168.103.100:26002")
rs.add("192.168.103.100:26003")

 

Mongos config (mongos.conf):

sharding:
  configDB: m103-csrs/192.168.103.100:26001,192.168.103.100:26002,192.168.103.100:26003
security:
  keyFile: /var/mongodb/pki/m103-keyfile
net:
  bindIp: localhost,192.168.103.100
  port: 26000
systemLog:
  destination: file
  path: /var/mongodb/db/mongos.log
  logAppend: true
processManagement:
  fork: true

 

Start the mongos server:

mongos -f mongos.conf

 

Connect to mongos:

vagrant@m103:~$ mongo --port 26000 --username m103-admin --password m103-pass --authenticationDatabase admin

 

Check sharding status:

MongoDB Enterprise mongos> sh.status()

 

Updated configuration for node1.conf:

sharding:
  clusterRole: shardsvr
storage:
  dbPath: /var/mongodb/db/node1
  wiredTiger:
    engineConfig:
      cacheSizeGB: .1
net:
  bindIp: 192.168.103.100,localhost
  port: 27011
security:
  keyFile: /var/mongodb/pki/m103-keyfile
systemLog:
  destination: file
  path: /var/mongodb/db/node1/mongod.log
  logAppend: true
processManagement:
  fork: true
replication:
  replSetName: m103-repl

 

Updated configuration for node2.conf:

sharding:
  clusterRole: shardsvr
storage:
  dbPath: /var/mongodb/db/node2
  wiredTiger:
    engineConfig:
      cacheSizeGB: .1
net:
  bindIp: 192.168.103.100,localhost
  port: 27012
security:
  keyFile: /var/mongodb/pki/m103-keyfile
systemLog:
  destination: file
  path: /var/mongodb/db/node2/mongod.log
  logAppend: true
processManagement:
  fork: true
replication:
  replSetName: m103-repl

 

Updated configuration for node3.conf:

sharding:
  clusterRole: shardsvr
storage:
  dbPath: /var/mongodb/db/node3
  wiredTiger:
    engineConfig:
      cacheSizeGB: .1
net:
  bindIp: 192.168.103.100,localhost
  port: 27013
security:
  keyFile: /var/mongodb/pki/m103-keyfile
systemLog:
  destination: file
  path: /var/mongodb/db/node3/mongod.log
  logAppend: true
processManagement:
  fork: true
replication:
  replSetName: m103-repl

 

Connecting directly to secondary node (note that if an election has taken place in your replica set, the specified node may have become primary):

mongo --port 27012 -u "m103-admin" -p "m103-pass" --authenticationDatabase "admin"

 

Shutting down node:

use admin
db.shutdownServer()

 

Restarting node with new configuration:

mongod -f node2.conf

 

Stepping down current primary:

rs.stepDown()

 

Adding new shard to cluster from mongos:

sh.addShard("m103-repl/192.168.103.100:27012")

 

 

 

 

What is true about the mongos?

- The mongos configuration file doesn't need to have a dbpath.

- The mongos configuration file needs to specify the config servers.

 

 

 

Chapter 3: Sharding

Lab: Deploy a Sharded Cluster

 

mongo --port 26000 -u "m103-admin" -p "m103-pass" --authenticationDatabase "admin"

sh.addShard("shard1/localhost:27001")

 

2 total, 2 passed, 0 skipped:
[PASS] "mongos is running"
[PASS] "shard1 has been added to cluster"

 

 

 

 

Chapter 3: Sharding

Config DB

 

use config

 

db.databases.find().pretty()

 

db.collections.find().pretty()

 

db.shards.find().pretty()

 

db.chunks.find().pretty()

 

db.mongos.find().pretty()

 

When should you manually write data to the Config DB?

- When directed to by MongoDB documentation or Support Engineers

 

 

Chapter 3: Sharding

Shard Keys

 

https://www.mongodb.com/docs/manual/core/sharding-shard-key/#change-a-document-s-shard-key-value

Shard Keys — MongoDB Manual

 

https://www.mongodb.com/docs/manual/core/sharding-shard-key/#refine-a-shard-key

Shard Keys — MongoDB Manual

 

use m103
show collections

sh.enableSharding("m103")

db.products.findOne()

db.products.createIndex( { "sku": 1 } )

sh.shardCollection( "m103.products", { "sku": 1 } )

sh.status()

 

Which of the following statements is true about shard keys?

- Shard keys are used to route queries to specific shards

- Shard keys must be supported by an index

 

 

Chapter 3: Sharding

Picking a Good Shard Key

Which of the following are indicators that a field or fields are a good shard key choice?

- Low Frequency

- High Cardinality

- Non-monotonic change

 

 

 

Chapter 3: Sharding

Hashed Shard Keys

Which of the following functions does Hashed Sharding support?

- Even distribution of a monotonically changing shard key field

 

 

Chapter 3: Sharding

Lab: Shard a Collection

 

mongoimport /dataset/products.json -d m103 -c products --drop --port 26000 --username m103-admin --password m103-pass --authenticationDatabase admin

sh.enableSharding("m103") 

db.products.createIndex({"name": 1})
db.adminCommand( { shardCollection: "m103.products", key: { name: 1 } } )
sh.status()

validate_lab_shard_collection

sh.addShard("m103-repl-2/localhost:27004")

 

 

2 total, 2 passed, 0 skipped:
[PASS] "The dataset is imported to m103.products"
[PASS] "m103.products uses the correct shard key"

 

 

 

Chapter 3: Sharding

Chunks

use config
show collections

db.chunks.findOne()

use config
db.settings.save({_id: "chunksize", value: 2})

sh.status()

mongoimport /dataset/products.part2.json --port 26000 -u "m103-admin" -p "m103-pass" --authenticationDatabase "admin" --db m103 --collection products

 

Which of the following is true about chunks?

- Chunk ranges have an inclusive minimum and an exclusive maximum.

 

 

Chapter 3: Sharding

Lab: Documents in Chunks

 

Consider the following document:

 

{
  "_id" : ObjectId("573f7197f29313caab89b3a4"),
  "sku" : 20005012,
  "name" : "Complete Hit Singles A's & B's - CD",
  "type" : "Music",
  "regularPrice" : 14.99,
  "salePrice" : 14.99,
  "shippingWeight" : "0.25"
}

 

Which of the following chunks would contain this document?

 

{
  "_id" : "m103.products-sku_20000000",
  "shard" : "shard2",
  "min" : {
    "sku" : 20000000
  },
  "max" : {
    "sku" : 25000000
  }
}

 

 

 

 

Chapter 3: Sharding

Balancing

 

https://www.mongodb.com/docs/manual/tutorial/manage-sharded-cluster-balancer/#sharding-schedule-balancing-window

Manage Sharded Cluster Balancer — MongoDB Manual

 

sh.startBalancer(timeout, interval)

 

sh.stopBalancer(timeout, interval)

 

sh.setBalancerState(boolean)

 

Given a sharded cluster running MongoDB 3.6, which of the shard components is responsible for running the Balancer process?

- Primary node of the Config Server Replica Set

 

 

 

Chapter 3: Sharding

Queries in a Sharded Cluster

 

 

https://www.mongodb.com/docs/manual/core/aggregation-pipeline-sharded-collections/

Aggregation Pipeline and Sharded Collections — MongoDB Manual

 

For a find() operation, which cluster component is responsible for merging the query results?

- The mongos that issued the query

 

 

 

Chapter 3: Sharding

Targeted Queries vs Scatter Gather: Part 1

 

db.products.find( { "sku": 20009151 } )

 

db.products.find( { "type": "movie" } )

 

{ "sku": 1, "type": 1, "name": 1 }

 

db.products.find( { "sku": ... } )
db.products.find( { "sku": ... , "type": ... } )
db.products.find( { "sku": ... , "type": ... , "name": ... } )

 

db.products.find( { "type": ... } )
db.products.find( { "name": ... } )

 

 

Chapter 3: Sharding

Targeted Queries vs Scatter Gather: Part 2

 

use m103
show collections

 

db.products.find({"sku" : 1000000749 }).explain()

 

db.products.find( {
  "name" : "Gods And Heroes: Rome Rising - Windows [Digital Download]" }
).explain()

 

 

Given a collection that is sharded on the following shard key:

{ "sku" : 1, "name" : 1 }

Which of the following queries results in a targeted query?

 

- db.products.find( { "name" : "MongoHacker", "sku" : 1337 } )

- db.products.find( { "sku" : 1337, "name" : "MongoHacker" } )

- db.products.find( { "sku" : 1337 } )

 

 

 

Chapter 3: Sharding

Lab: Detect Scatter Gather Queries

Which of the following is required in order for a query to be targeted to a subset of shards?

- An index exists on the shard key

- The query uses the shard key

 

 

Final Exam

Final: Question 1

 

Which of the following are valid command line instructions to start a mongod? You may assume that all specified files already exist.

mongod -f /etc/mongod.conf

mongod --logpath /var/log/mongo/mongod.log --dbpath /data/db --fork

 

 

Final Exam

Final: Question 2

storage:
  dbPath: /data/db
systemLog:
  destination: file
  path: /var/log/mongod.log
net:
  bindIp: localhost,192.168.0.100
security:
  keyFile: /var/pki/keyfile
processManagement:
  fork: true

 

Select all the directories that MongoDB must have access to. Disregard the path to the configuration file itself, and the /tmp/ directory.

 

- /var/log/

- /var/pki/

- /data/db/

 

 

Final Exam

Final: Question 3

Given the following output from rs.status().members:

 

[
  {
    "_id": 0,
    "name": "localhost:27017",
    "health": 1,
    "state": 1,
    "stateStr": "PRIMARY",
    "uptime": 548,
    "optime": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDate": ISODate("2018-03-14T14:47:51Z"),
    "electionTime": Timestamp(1521038358, 2),
    "electionDate": ISODate("2018-03-14T14:39:18Z"),
    "configVersion": 2,
    "self": true
  },
  {
    "_id": 1,
    "name": "localhost:27018",
    "health": 1,
    "state": 2,
    "stateStr": "SECONDARY",
    "uptime": 289,
    "optime": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDurable": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDate": ISODate("2018-03-14T14:47:51Z"),
    "optimeDurableDate": ISODate("2018-03-14T14:47:51Z"),
    "lastHeartbeat": ISODate("2018-03-14T14:47:56.558Z"),
    "lastHeartbeatRecv": ISODate("2018-03-14T14:47:56.517Z"),
    "pingMs": NumberLong("0"),
    "syncingTo": "localhost:27022",
    "configVersion": 2
  },
  {
    "_id": 2,
    "name": "localhost:27019",
    "health": 1,
    "state": 2,
    "stateStr": "SECONDARY",
    "uptime": 289,
    "optime": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDurable": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDate": ISODate("2018-03-14T14:47:51Z"),
    "optimeDurableDate": ISODate("2018-03-14T14:47:51Z"),
    "lastHeartbeat": ISODate("2018-03-14T14:47:56.558Z"),
    "lastHeartbeatRecv": ISODate("2018-03-14T14:47:56.654Z"),
    "pingMs": NumberLong("0"),
    "syncingTo": "localhost:27022",
    "configVersion": 2
  },
  {
    "_id": 3,
    "name": "localhost:27020",
    "health": 1,
    "state": 2,
    "stateStr": "SECONDARY",
    "uptime": 289,
    "optime": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDurable": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDate": ISODate("2018-03-14T14:47:51Z"),
    "optimeDurableDate": ISODate("2018-03-14T14:47:51Z"),
    "lastHeartbeat": ISODate("2018-03-14T14:47:56.558Z"),
    "lastHeartbeatRecv": ISODate("2018-03-14T14:47:56.726Z"),
    "pingMs": NumberLong("0"),
    "syncingTo": "localhost:27022",
    "configVersion": 2
  },
  {
    "_id": 4,
    "name": "localhost:27021",
    "health": 0,
    "state": 8,
    "stateStr": "(not reachable/healthy)",
    "uptime": 0,
    "optime": {
      "ts": Timestamp(0, 0),
      "t": NumberLong("-1")
    },
    "optimeDurable": {
      "ts": Timestamp(0, 0),
      "t": NumberLong("-1")
    },
    "optimeDate": ISODate("1970-01-01T00:00:00Z"),
    "optimeDurableDate": ISODate("1970-01-01T00:00:00Z"),
    "lastHeartbeat": ISODate("2018-03-14T14:47:56.656Z"),
    "lastHeartbeatRecv": ISODate("2018-03-14T14:47:12.668Z"),
    "pingMs": NumberLong("0"),
    "lastHeartbeatMessage": "Connection refused",
    "configVersion": -1
  },
  {
    "_id": 5,
    "name": "localhost:27022",
    "health": 1,
    "state": 2,
    "stateStr": "SECONDARY",
    "uptime": 289,
    "optime": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDurable": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDate": ISODate("2018-03-14T14:47:51Z"),
    "optimeDurableDate": ISODate("2018-03-14T14:47:51Z"),
    "lastHeartbeat": ISODate("2018-03-14T14:47:56.558Z"),
    "lastHeartbeatRecv": ISODate("2018-03-14T14:47:55.974Z"),
    "pingMs": NumberLong("0"),
    "syncingTo": "localhost:27017",
    "configVersion": 2
  },
  {
    "_id": 6,
    "name": "localhost:27023",
    "health": 1,
    "state": 2,
    "stateStr": "SECONDARY",
    "uptime": 289,
    "optime": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDurable": {
      "ts": Timestamp(1521038871, 1),
      "t": NumberLong("1")
    },
    "optimeDate": ISODate("2018-03-14T14:47:51Z"),
    "optimeDurableDate": ISODate("2018-03-14T14:47:51Z"),
    "lastHeartbeat": ISODate("2018-03-14T14:47:56.558Z"),
    "lastHeartbeatRecv": ISODate("2018-03-14T14:47:56.801Z"),
    "pingMs": NumberLong("0"),
    "syncingTo": "localhost:27022",
    "configVersion": 2
  }
]

 

At this moment, how many replica set members are eligible to become primary in the event of the current Primary crashing or stepping down?

- 5

 

 

Final Exam

Final: Question 4

Given the following replica set configuration:

 

conf = {
  "_id": "replset",
  "version": 1,
  "protocolVersion": 1,
  "members": [
    {
      "_id": 0,
      "host": "192.168.103.100:27017",
      "priority": 2,
      "votes": 1
    },
    {
      "_id": 0,
      "host": "192.168.103.100:27018",
      "priority": 1,
      "votes": 1
    },
    {
      "_id": 2,
      "host": "192.168.103.100:27018",
      "priority": 1,
      "votes": 1
    }
  ]
}

 

What errors are present in the above replica set configuration?

- You cannot specify the same host information among multiple members.

- You cannot specify two members with the same _id.

 

 

 

Final Exam

Final: Question 5

Given the following replica set configuration:

 

conf = {
  "_id": "replset",
  "version": 1,
  "protocolVersion": 1,
  "members": [
    {
      "_id": 0,
      "host": "localhost:27017",
      "priority": 1,
      "votes": 1
    },
    {
      "_id": 1,
      "host": "localhost:27018",
      "priority": 1,
      "votes": 1
    },
    {
      "_id": 2,
      "host": "localhost:27019",
      "priority": 1,
      "votes": 1
    },
    {
      "_id": 3,
      "host": "localhost:27020",
      "priority": 0,
      "votes": 0,
      "slaveDelay": 3600
    }
  ]
}

 

What is the most likely role served by the node with "_id": 3?

- It serves as a "hot" backup of data in case of accidental data loss on the other members, like a DBA accidentally dropping the database.

 

 

Final Exam

Final: Question 6

Given the following shard key:

 

{ "country": 1, "_id": 1 }

 

Which of the following queries will be routed (targeted)? Remember that queries may be routed to more than one shard.

 

db.customers.find({"country": "Norway", "_id": 54})

db.customers.find({"country": { $gte: "Portugal", $lte: "Spain" }})

db.customers.find({"_id": 914, "country": "Sweden"})