index creation: MongoDB

Lets learn to create index and to optimize the database in MongoDB.

Creating “Database”: “temp”, “Collection”: “no”, and inserting 10 Million documents inside it

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use temp
switched to db temp
 
for(i=0; i< = 10000000; i++)
db.no.insert({"student_id": i, "name": "Satish"});

Since Mongo Shell is built out of JavaScript, you can pass in any valid Javascript code to it. So we write a for loop and insert 10 Million documents inside “no” collection.

creating-index-mongodb

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MongoDB shell version: 2.6.1
connecting to: test
> show dbs
admin    (empty)
daily    0.078GB
local    0.078GB
nesting  0.078GB
school   0.078GB
temp     3.952GB
test     0.078GB
> use temp
switched to db temp
> show collections
no
system.indexes
> db.no.find().pretty()
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cda"),
        "student_id" : 0,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cdb"),
        "student_id" : 1,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cdc"),
        "student_id" : 2,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cdd"),
        "student_id" : 3,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cde"),
        "student_id" : 4,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cdf"),
        "student_id" : 5,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce0"),
        "student_id" : 6,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce1"),
        "student_id" : 7,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce2"),
        "student_id" : 8,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce3"),
        "student_id" : 9,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce4"),
        "student_id" : 10,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce5"),
        "student_id" : 11,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce6"),
        "student_id" : 12,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce7"),
        "student_id" : 13,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce8"),
        "student_id" : 14,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ce9"),
        "student_id" : 15,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cea"),
        "student_id" : 16,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ceb"),
        "student_id" : 17,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cec"),
        "student_id" : 18,
        "name" : "Satish"
}
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833ced"),
        "student_id" : 19,
        "name" : "Satish"
}
Type "it" for more
 
> it

“no” collection has 10 Million record, but it won’t fetch you all records at once, as it would take a lot of time and resources of your computer! So it only fetches 20 records at a time. You can iterate through next 20 documents by using command “it“.

index creation: MongoDB



YouTube Link: https://www.youtube.com/watch?v=zK_mRyiNs-I [Watch the Video In Full Screen.]



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> db.no.find({"student_id": 5}).pretty()
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cdf"),
        "student_id" : 5,
        "name" : "Satish"
}
 
 
> db.no.findOne({"student_id": 5});
{
        "_id" : ObjectId("53c9020abcdd1ea7fb833cdf"),
        "student_id" : 5,
        "name" : "Satish"
}
> db.no.find({"student_id": 5000000}).pretty()
{
        "_id" : ObjectId("53c90ca6bcdd1ea7fbcf881a"),
        "student_id" : 5000000,
        "name" : "Satish"
}

find() method scans through all the documents present in the collection to find multiple matches for the condition. So in above case, find() method scans through 10 Million documents, hence returns the result slowly. Where as findOne() method stops scanning the collection as soon as it finds the first matching document, so findOne() returns result faster than find() method.

Related Read:
Multi-key Index: MongoDB
index / key: MongoDB

Creating index

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> show collections
no
system.indexes
 
> db.system.indexes.find()
{ "v" : 1, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "temp.no" }
 
> db.no.ensureIndex({"student_id": 1});
{
        "createdCollectionAutomatically" : false,
        "numIndexesBefore" : 1,
        "numIndexesAfter" : 2,
        "ok" : 1
}
 
> db.system.indexes.find()
{ "v" : 1, "key" : { "_id" : 1 }, 
                     "name" : "_id_", "ns" : "temp.no" }
{ "v" : 1, "key" : { "student_id" : 1 }, 
                     "name" : "student_id_1", "ns" : "temp.no" }

We create index on “student_id”. It takes little time to create the index, as we have 10 Million documents inside “no” collection.

After creating index on “student_id”, run the same command and you’ll get the results instantly – maybe it takes 0.01 ms, but the delay can’t be noticed.
Why does it return results faster after creating index on “student_id”? Watch this short video lesson to know it: index / key: MongoDB

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> db.no.find({"student_id": 5000000}).pretty()
{
        "_id" : ObjectId("53c90ca6bcdd1ea7fbcf881a"),
        "student_id" : 5000000,
        "name" : "Satish"
}
> db.no.find({"student_id": 10000000}).pretty()
{
        "_id" : ObjectId("53c914adbcdd1ea7fb1bd35a"),
        "student_id" : 10000000,
        "name" : "Satish"
}
>

So the querys/commands can be optimized by creating indexes on frequently accessed fields.

Optimize / Improve Performance of jQuery Applications

Video tutorial illustrating simple tweaks which help optimize / improve the performance of jQuery Applications.

To Optimize
1. Write all javascript programs in an external file and embed it into the html pages.
2. Whenever possible, embed the javascript file at the end of body tag. i.e., just before the closing body tag.
3. It’s also good practice to separate CSS coding to an external file and then embed it to the web pages.

How it helps ?
1. i. If you have thousands of web pages, writing the same code on all the pages and maintaining it and/or modifying it is a touch job.
Having it in an external file helps in re-usability and maintainability.
ii. It only loads the javascript files once and do not load the same files again and again for all other pages, hence saving a lot of bandwidth. Also highly optimizing the load time of web pages.
2. When the parser encounters these javascript files, they stop loading all other elements and allocate all its bandwidth to load javascript file. So writing it at the end of body tag helps. Since all other important elements like images, content will be loaded before these time-consuming javascript files.

Video Tutorial: Optimize / Improve Performance of jQuery Applications



YouTube Link: https://www.youtube.com/watch?v=BsPgkr-YGMs [Watch the Video In Full Screen.]



Above video uses Animation of Text and Image: jQuery code to illustrate the optimization concept. If you have not already seen the video, we highly encourage you to watch it and practice it.

In our future tutorials we will be writing most of our javascript code in external file and will be embedding them at the end of body tag. With this tutorial you know why we would do that!