The document provides an agenda for a presentation on getting expertise with MongoDB design patterns. It includes sections on MongoDB recap, how MongoDB works, the _id field, query execution order, indexes, replication, sharding, and introduces the presenters.

1. Get Expertise with
MongoDB
Design Pattern

2. Agenda
★ MongoDB Recap
★ How mongoDB works?
★ The _id
★ In n Out of Query Execution.
★ Indexes
★ What is Replication?
★ What is Sharding ?

3. About Us
Amit Thakkar
Tech Blogger @
CodeChutney.in
JavaScript Lover
Working on MEAN Stack
Twitter: @amit_thakkar01
LinkedIn: linkedin.com/in/amitthakkar01
Facebook: facebook.com/amit.thakkar01
Vibhor Kukreja
JavaScript Ninja
Working on MEAN Stack
Twitter: @VibhorKukreja
Email : vibhor.kukreja@intelligrape.com

4. MongoDB Recap
1. No-Sql Database.
2. Installation.
3. Basic CRUD operation.
4. Stores data in JSON.
5. Schemaless.
6. Great Performance.
7. No Joins.
8. Easily scalable.

5. MongoDB Recap

6. How mongoDB works?
There is a process “mongod” that acts as a database server.
This process attaches itself to a directory with the --dbpath option. The default
dbpath is “/data/db”.
And start listening to a specific port number via --port option.The default port is
27017.
> mongod --dbpath ~/testDB --port 28080
You just need to create the testDB directory before allocating it to the
mongod process.

8. Look what’s inside the created dbpath ?
- /journal
- test.ns // namespace for database
- test.0 // raw data storage files
- test.1 // raw data storage files
But what is this journal directory for?

9. Journal Option
Journal option does a write ahead logging to an ondisk
journal to guarantee write operation. i.e write in memory
and on-disk journal before in the data file. ( Data
Consistency )
Where can we set this option?
There is an configuration file for the mongod process.
> cat /etc/mongodb.conf

10. How to get connected with mongod?
There are two modes to interact with the DB.
1. mongoDB Driver/Plugin
- Node.js (mongoose)
- Grails (GORM)
- Python (pymongo)
2. mongo Shell - supports javascript <3

11. mongo Shell
To connect a mongo shell process with our mongod process, we just have to
specify the port number on which the mongod process is listening.
> mongo --port 28080
To check the status of our mongo server, for a proper analysis we must start
the mongostat process to check the server request/response.
> mongostat --port 28080

12. Yeah !! Our Single instance Server is
Up and Running.
At this point of time , we have just created a single
mongoDB server along with a mongo shell that
interacts with this mongoDB server.

13. The _id
It can be represented as a primary key in an collection.
The mongo _id have few properties like,
It must be unique.
It can store any type of data, except boolean and array.
eg - _id : “intelligrape”
_id : { “company” : “intelligrape” }
_id : 17
_id : true //You can do this, but in this case you can have only two records in this collection
By default it stores ObjectId(“HexString”), and it gives a unique value every time as it is computed with
the help of the following.
● The first 4 bytes representing the seconds
● The next 3 bytes are the machine identifier
● The next 2 bytes consists of process id
● The last 3 bytes are a random counter value

14. _id impact on save() and insert() Query
save( ) - is risky :P
If there is an particular insert key already present in the collection, then it will
replace that old document completely from the collection with the new one.
( without even prompting it :D )
So, it may become risky to use save query in our Applications. Its better to use
the insert() query as it throws “duplicate key error index” error.

15. Importing a document in mongoDB
We can easily import a document in mongoDB. Mongo itself provides a process to
import document.
> mongoimport --db test --port 28080 --type json --collection person < testColl.json
--db defines the database name
--port server port number
--type document type, which is to be import
--collection name of the collection, where insertion is to be done

16. PowerOf2Sizes ( v2.6 +)
What is move and padding in mongoDB storage?
> db.runCommand({ collMod : ”collection_Name”,usePowerOf2Sizes : true })

17. In n Out of Query Execution.
> db.person.find({}).sort({name:1}).skip(2).limit(3);
> db.person.find({}).skip(2).sort({name:1}).limit(3);
> db.person.find({}).limit(3).skip(2).sort({name:1});
What impact does they will make, on the result?

19. Bulk Write Operations ( v2.6+)
Type of bulk operations -
● Ordered
● Unordered
> var bulk = db.person.initializeUnorderedBulkOp();
> bulk.insert( { name : ”Joe” } );
> bulk.insert( { name : ”Tim” } );
> bulk.insert( { name : ”Steve” } );
> bulk.execute();

20. What is an Index?
A data structure that can be used to make certain
queries more efficient.

22. How can we index ?
An index on _id is automatic. For more, ensureIndex :
> db.posts.ensureIndex({“name”:1});
> db.posts.ensureIndex({name: 1, date: ‐1});
> db.posts.ensureIndex({title: 1},{unique: true, sparse:true,dropDups:true});
> db.posts.ensureIndex(...,{background: true});
> db.posts.ensureIndex({“comments.author”: 1});
{“tags”: [“mongodb”, “indexing”], ...}
> db.posts.ensureIndex({“tags”: 1}); // multikey
> db.posts.ensureIndex({“location”: “2d”}); //geospatial
db.post.find({title:”mongo”}).hint({name:1,title:1});

23. What is Replication?
● Replication is the process of synchronizing data across
multiple servers.
● Mongo achieves Replication through Replica Sets
● Replica sets are a form of asynchronous master/slave
replication
● A replica set consists of two or more nodes that are
copies of each other. (i.e.: replicas)

25. Purpose of Replication
● Automated Failover / High Availability
If primary fails then replica set will
attempt to select another member
to become the new primary.
Use heartbeat signal to detect failure

26. ● Distributed Read Load/Read Scaling
By default, the primary node of a replica set is accessed for
all reads and writes.
● Disaster Recovery
So, you have a pool of servers with one primary (the
master) and N secondaries (slaves). If the primarycrashes
or disappears, the other servers will hold an election to
choose a new primary. Arbiter helps to achieve >50 votes
in case of draw.
connectionString = (“mongodb://localhost:37017", replicaSet="s0",w=4,
j=True)

27. Lets Create a Replica Set :P
mkdir -p ~/tempDB/rs1 ~/tempDB/rs2 ~/tempDB/rs3
mongod --replSet m101 --logpath "1.log" --dbpath ~/tempDB/rs1 --port
47017 --fork
mongod --replSet m101 --logpath "2.log" --dbpath ~/tempDB/rs2 --port
47018 --fork
mongod --replSet m101 --logpath "3.log" --dbpath ~/tempDB/rs3 --port
47019 --fork
Seperate mongod processes have been created, lets connect them with
each other.

28. Configuring Replica Sets.
> mongo --port 47017
config = { _id: "m101", members:[
{ _id : 0, host : "localhost:47017"},
{ _id : 1, host : "localhost:47018"},
{ _id : 2, host : "localhost:47019"} ]
};
rs.initiate(config);
rs.status();

31. What is Sharding ?

33. Lets Create Shards :P
Shard 0
mkdir -p ~/testDB/shard0/rs0 ~/testDB/shard0/rs1 ~/testDB/shard0/rs2
mongod --replSet s0 --logpath "testDB/s0-r0.log" --dbpath ~/testDB/shard0/rs0 --port 37017 --fork --
shardsvr
mongod --replSet s0 --logpath "testDB/s0-r1.log" --dbpath ~/testDB/shard0/rs1 --port 37018 --fork --
shardsvr
mongod --replSet s0 --logpath "testDB/s0-r2.log" --dbpath ~/testDB/shard0/rs2 --port 37019 --fork --
shardsvr
mongo --port 37017
config = { _id: "s0", members:[
{ _id : 0, host : "localhost:37017" },
{ _id : 1, host : "localhost:37018" },
{ _id : 2, host : "localhost:37019" }]};
rs.initiate(config);

34. Shard 1
mkdir -p ~/testDB/shard1/rs0 ~/testDB/shard1/rs1 ~/testDB/shard1/rs2
mongod --replSet s1 --logpath "testDB/s1-r0.log" --dbpath ~/testDB/shard1/rs0 --port 47017 --fork --
shardsvr
mongod --replSet s1 --logpath "testDB/s1-r1.log" --dbpath ~/testDB/shard1/rs1 --port 47018 --fork --
shardsvr
mongod --replSet s1 --logpath "testDB/s1-r2.log" --dbpath ~/testDB/shard1/rs2 --port 47019 --fork --
shardsvr
mongo --port 47017
config = { _id: "s1", members:[
{ _id : 0, host : "localhost:47017" },
{ _id : 1, host : "localhost:47018" },
{ _id : 2, host : "localhost:47019" }]};
rs.initiate(config);

35. Shard 2
mkdir -p ~/testDB/shard2/rs0 ~/testDB/shard2/rs1 ~/testDB/shard2/rs2
mongod --replSet s2 --logpath "testDB/s2-r0.log" --dbpath ~/testDB/shard2/rs0 --port 57017 --fork --
shardsvr
mongod --replSet s2 --logpath "testDB/s2-r1.log" --dbpath ~/testDB/shard2/rs1 --port 57018 --fork --
shardsvr
mongod --replSet s2 --logpath "testDB/s2-r2.log" --dbpath ~/testDB/shard2/rs2 --port 57019 --fork --
shardsvr
mongo --port 57017
config = { _id: "s2", members:[
{ _id : 0, host : "localhost:57017" },
{ _id : 1, host : "localhost:57018" },
{ _id : 2, host : "localhost:57019" }]};
rs.initiate(config);

36. Congif Servers
mkdir -p ~/testDB/config/config-a ~/testDB/config/config-b ~/testDB/config/config-c
mongod --logpath "testDB/cfg-a.log" --dbpath ~/testDB/config/config-a --port 57040 -
-fork --configsvr
mongod --logpath "testDB/cfg-b.log" --dbpath ~/testDB/config/config-b --port 57041 -
-fork --configsvr
mongod --logpath "testDB/cfg-c.log" --dbpath ~/testDB/config/config-c --port 57042 -
-fork --configsvr

37. Setting Up “mongos”
mongos --logpath "testDB/mongos-1.log" --port 28888 --configdb
localhost:57040,localhost:57041,localhost:57042 --fork
mongo --port 28888
db.adminCommand( { addshard : "s0/"+"localhost:37017" } );
db.adminCommand( { addshard : "s1/"+"localhost:47017" } );
db.adminCommand( { addshard : "s2/"+"localhost:57017" } );
db.adminCommand({enableSharding: "test"}) // test is the db name
db.adminCommand({shardCollection: "test.grades", key: {month:1,student_id:1}});

38. Exercise Time

39. Congo !! Your Shard
environment is up
and running :)

40. Question Answer??