WEEK 6 :APPLICATION ENGINEERING : M101P: MONGODB FOR DEVELOPERS

Homework 6.1

Which of the following statements are true about replication in MongoDB? Check all that apply.

Solution : Here you find updated answer with two possible outcomes as follow

Homework 6.2

Let's suppose you have a five member replica set and want to assure that writes are committed to the journal and are acknowledged by at least 3 nodes before you proceed forward. What would be the appropriate settings for w and j?

Solution : 

Homework 6.3

Which of the following statements are true about choosing and using a shard key?

Solution : There are three possibly true statement for this homework.

Homework 6.4

You have a sharded system with three shards and have sharded the collections "students" in the "school" database across those shards. The output of sh.status() when connected to mongos looks like this:

mongos> sh.status()
--- Sharding Status ---
  sharding version: {
    "_id" : 1,
    "minCompatibleVersion" : 5,
    "currentVersion" : 6,
    "clusterId" : ObjectId("5531512ac723271f602db407")
}
  shards:
    {  "_id" : "s0",  "host" : "s0/localhost:37017,localhost:37018,localhost:37019" }
    {  "_id" : "s1",  "host" : "s1/localhost:47017,localhost:47018,localhost:47019" }
    {  "_id" : "s2",  "host" : "s2/localhost:57017,localhost:57018,localhost:57019" }
  balancer:
    Currently enabled:  yes
    Currently running:  yes
        Balancer lock taken at Fri Apr 17 2015 14:32:02 GMT-0400 (EDT) by education-iMac-2.local:27017:1429295401:16807:Balancer:1622650073
    Collections with active migrations:
        school.students started at Fri Apr 17 2015 14:32:03 GMT-0400 (EDT)
    Failed balancer rounds in last 5 attempts:  0
    Migration Results for the last 24 hours:
        2 : Success
        1 : Failed with error 'migration already in progress', from s0 to s1
  databases:
    {  "_id" : "admin",  "partitioned" : false,  "primary" : "config" }
    {  "_id" : "school",  "partitioned" : true,  "primary" : "s0" }
        school.students
            shard key: { "student_id" : 1 }
            chunks:
                s0  1
                s1  3
                s2  1
            { "student_id" : { "$minKey" : 1 } } -->> { "student_id" : 0 } on : s2 Timestamp(3, 0)
            { "student_id" : 0 } -->> { "student_id" : 2 } on : s0 Timestamp(3, 1)
            { "student_id" : 2 } -->> { "student_id" : 3497 } on : s1 Timestamp(3, 2)
            { "student_id" : 3497 } -->> { "student_id" : 7778 } on : s1 Timestamp(3, 3)
            { "student_id" : 7778 } -->> { "student_id" : { "$maxKey" : 1 } } on : s1 Timestamp(3, 4)

Solution : S1

Homework 6.5

In this homework you will build a small replica set on your own computer. We will check that it works with validate.py, which you should download from the Download Handout link.
Create three directories for the three mongod processes. On unix, this could be done as follows:

mkdir -p /data/rs1 /data/rs2 /data/rs3

Now start three mongo instances as follows. Note that are three commands. The browser is probably wrapping them visually.

mongod --replSet m101 --logpath "1.log" --dbpath /data/rs1 --port 27017 --smallfiles --oplogSize 64 --fork

mongod --replSet m101 --logpath "2.log" --dbpath /data/rs2 --port 27018 --smallfiles --oplogSize 64 --fork

mongod --replSet m101 --logpath "3.log" --dbpath /data/rs3 --port 27019 --smallfiles --oplogSize 64 --fork

Windows users: Omit -p from mkdir. Also omit --fork and use start mongod with Windows compatible paths (i.e. backslashes "\") for the --dbpath argument (e.g; C:\data\rs1).
Now connect to a mongo shell and make sure it comes up

Now you will create the replica set. Type the following commands into the mongo shell:

config = { _id: "m101", members:[
          { _id : 0, host : "localhost:27017"},
          { _id : 1, host : "localhost:27018"},
          { _id : 2, host : "localhost:27019"} ]
};
rs.initiate(config);

At this point, the replica set should be coming up. You can type

rs.status()

to see the state of replication.
Now run validate.py to confirm that it works.

python validate.py

Validate connects to your local replica set and checks that it has three nodes. It has been tested under Pymongo 2.3 and 2.4. Type the validation code below.

Solution :kjvjkl3290mf0m20f2kjjv

At the end I just want to say if you want to learn mongoDB, First practice with youself. because no one can steel talent 😇