u.2.5.3 - cassandra

// LESSON 1.1 - INTRO TO CASSANDRA 
what is cassandra 
    - highly scalable, high performacne, distributed nosql database
    - designed to handle huge amount of data across many commodity servers, providing hgih availability without a single point of failure
    - column oriented nosql database 
    - fault tolerant meaning suppose there are 4 nodes in a cluster, here each node has a copy of same data, if one node is no longer serving then other three nodes can served as per request  
    - supports acid property (atomicity, consistency, isolation and durability)
cassandra architecture: cassandra was designed to handle big data workload across multiple nodes without a single point of failure 
    - in Cassandra, each node is independent and at the same time interconnected to other nodes. All the nodes in a cluster play the same role
    - every node in a cluster can accept, read, and write requests, regardless of where the data is actually located in the cluster 
    - in the case of failure of one node, read/write requests can be served from other nodes in the network 
components of cassandra 
    node: place where data is stored  
    data center: collection of related nodes  
    cluster: component which contains one or more data centers 
    commit log: crash-recovery mechanism, every write operation is written to the comit log  
    mem-table: memory resident data structure. after commit log, the data will be written to the mem-table. Sometimes, for a single-column fmaily there wil be multiple mem-tables 
    sstable: disk file to which the data is flushed from the mem-table when its contents reach a threshold value 
    bloom filter: quick, nondeterministic, algorithms for testing whether an element is a member of a set. special kind of cache. bloom filters are accessed after every query 
cql (cassandra query language)
    - used to access cassandra through its nodes 
    - client can approach any of the nodes for their read-write operations, that node (coordinator) plays a proxy between the client and the nodes holding the data 

    write operations 
        write data -> commit log(inside memory disk) -> memtable(outside memory disk) -> flush to sstable(inside memory disk)
    read operations 
        - cassandra gets values from the mem-table and checks the bloom filter to find the appropriate sstable which contains the required data 
unfinished - data model 

// LESSON 1.2 - CASSANDRA KEYSPACE: equivalent to database in rdbms  
create keyspace 
    CREATE KEYSPACE keyspace_name 
    WITH replication = {'class':'SimpleStrategy', 'replication_factor' : 3}; // WITH replicaton={'class':strategy name,'replication_factor': no_of_replications_on_different_nodes}
    [AND DURABLE_WRITES = false;] // default is set to true, just don't touch this at all
    strategies 
        SimpleStrategy: used in the case of one data center  
        NetworkTopologyStrategy: used in the case of more than one data centers 
    replication factor: number of replicas of data places on different nodes 
alter keyspace 
    ALTER KEYSPACE keyspace_name 
    WITH replication = {'class':'SimpleStrategy', 'replication_factor' : 3}; // WITH replicaton={'class':strategy name,'replication_factor': no_of_replications_on_different_nodes}
    [WITH DURABLE_WRITES = false;] 
drop keyspace 
    DROP KEYSPACE keyspace_name 

// UNFINISHED - INDEX - LESSON 1.3 - CASSANDRA TABLE INDEX 
create table 
    CREATE TABLE tablename(  
        column1_name uuid PRIMARYKEY,  // column_name datatype constraint
        column2_name double,  // column_name datatype
        column3_name float 
    )  
alter table 
    adding new column 
        ALTER TABLE table_name  
        ADD new_column_name text; // ADD new_column_name datatype; 
drop table: remove the table as a whole 
    DROP TABLE table_name 
truncate table: all the rows of the table are all deleted permanently 
    TRUNCATE table_name 
create index 
    
drop index 

cassandra batch: used to execute multiple modification statements (insert, update, delete) 
    BEGIN BATCH 
        // enter multiple statements here 
        INSERT INTO table_name(column_name1, column_name2) VALUES (1,2)
        UPDATE table_name SET column_name = 1 WHERE column_id = 1;
    APPLY BATCH 
    
// LESSON 1.4 - CASSANDRA QUERY (CQL)
create data 
    INSERT INTO table_name 
    (column_name1, column_name2) 
    VALUES (value_1, value_2); 
read data 
    SELECT column_name FROM table_name;
update data 
    UPDATE keyspace_name.table_name 
    SET column_name1 = value1,
        column_name2 = value2
    WHERE column_id = 1;
delete data 
    DELETE FROM table_name 
    WHERE column_name = value; // WHERE [condition]  

// UNFINISHED - EXPLAIN EACH DATATYPE - LESSON 1.5 - CASSANDRA CQL TYPES 
data types 
    ascii 
    bigint 
    blob 
    boolean 
    counter 
    double 
    float 
    frozen 
    inet 
    int 
    list 
    map 
    set text 
    timestamp 
    timeuuid 
    tuple 
    uuid 
    varchar 
    varint