Database - MongoDB

MongoDB Design patterns based on application usage perspective:
    The scheme depends on your application use case
        Data Access Patterns
        Number of reading vs update
        what is the size of expected documents


Performance issues in MongoDB:
    Schema Design:
    {
        Inherently slow operation
        Blocked waiting for a slow operation
    }
    Insufficient or poorly tuned hardware

Design for :

    Simplicity
    Performance
    Scalability

Index makes faster = Effiecenit execution
    many indexes extra memory and slow down
    do not change index field because has to rebuild indexing again

Aggregation is a pipeline until output comes out stage by stage- 25 stages
    $match - get results
    $unwind - create separate documents from array
    $group - group data
    $project -> rename fields
    $lookup - join
    $indexState - index status
    $out - storing result into new collection

    $sort
    $limit
    $skip

Advantages:

    Faster because of No join at run time and less code
    Flexible schema structure
    Scalable
    Handle messy Data
    Combine different data from a different source

RDBMS

Database Normalization
    1. Avoid data redundancy - repeative data
    2. Ensure data integrity - Should able to CURD without negative affect on other data

Normalization:
    Process of organizing database to avoid data redundancy and ensure data integrity.

1NF
    1.each record represent one primary key
    2.one columns should have single value ( atomic values)
    3. no repeating groups - example class1, class2 ,class3

2NF
    no partial dependacies - non primary columns should depeding only on primary column
    Problem: lead to data redundancy

    student_id	class_id	teacher
    1	            1	    Smith
    1	            2	    Jackson
    2	            3	    James
    2	            2	    Jackson

    teacher is not depending on one primary key

3NF
    There are no transitive dependencies.
        Problem: lead to data redundancy
            A determines B
            B does not determine A
            B determines C

        id	class_name	teacher	office
        1	Math	    Smith	 A107
        2	Programming	Jackson	 B205
        3	History	    James	 A100
        4	Science	    Jackson	 B205

    teach is not determine id and class so create them into separate table