Community Articles
Find and share helpful community-sourced technical articles
Announcements
Alert: Welcome to the Unified Cloudera Community. Former HCC members be sure to read and learn how to activate your account here.
Labels (1)
Expert Contributor

Prerequisites

  • 1)Download HDP Sandbox
  • 2)MySQL database (Should already be present in the sandbox)
  • 3)Nifi 0.6 or later ( Download and install a new version of NIFI or use Ambari to install NIFI in the sandbox)

MySQL setup (Source Database)

In this setup we will create a table in MySQL tables and create a few triggers on the tables to emulate transactions.

  • These triggers will find out if the change introduced was an insert or an update
  • also will update the time stamp on the updated/inserted row. ( This is very important as Nifi Will be polling on this column to extract changes based on the time stamp)
unix> mysql –u root –p
unix>Enter
password:<enter>
mysql>
mysql> create database
test_cdc;
mysql> create user
'test_cdc'@'localhost' identified by 'test_cdc';
mysql> GRANT ALL
PRIVILEGES ON *.* TO 'test_CDC'@'%' IDENTIFIED BY 'test_CDC' WITH GRANT OPTION;
mysql>Flush Privileges
mysql> exit;
unix> mysql –u test_cdc –p
test_cdc
mysql>create table CDC_TEST
(
Column_A int, 
Column_B text, 
Created_date datetime,
INFORMATION text
);

Create Triggers in MYSQL

      mysql> create trigger CDC_insert 
       before insert on
       cdc_test
       for each row
       set 
          NEW.created_date =NOW()
        , NEW.information = 'INSERT';
mysql> create trigger CDC_UPDATE  
        before update on 
        cdc_test
        for each row
    set 
      NEW.created_date = NOW()
     , NEW.information = 'UPDATE';

HIVE setup (Destination Database)

In hive, we have created an external table, with exactly same data structure as MySQL table, NIFI would be used to capture changes from the source and insert them into the Hive table.

Using AMBARI Hive view or from HIVE CLI create the following table in the hive default database:

I have used hive cli to create the table:

Unix> hive   Hive> create external table
                         HIVE_TEST_CDC   
                         (   COLUMN_A int ,   
                             COLUMN_B string,  
                             CREATED_DATE string, 
                              INFORMATION string)   
stored as avro   
location '/test-nifi/CDC/'

Note: I am not including how to create Managed Hive table with ORC format, that would be covered in a different article.

Nifi Setup :

This is a simple NIFI setup, the queryDatabase table processor is only available as part of default processors from version 0.6 of Nifi.

7436-screen-shot-2016-09-07-at-14215-pm.png

queryDatabaseProcessor Configuration

Its very intuitive

7438-screen-shot-2016-09-07-at-14635-pm.png

The main things to configure is DBCPConnection Pool and Maximum-value Columns

Please choose this to be the date-time stamp column that could be a cumulative change-management column

This is the only limitation with this processor as it is not a true CDC and relies on one column. If the data is reloaded into the column with older data the data will not be replicated into HDFS or any other destination.

This processor does not rely on Transactional logs or redo logs like Attunity or Oracle Goldengate. For a complete solution for CDC please use Attunity or Oracle Goldengate solutions.

DBCPConnectionPool Configuration:

7437-screen-shot-2016-09-07-at-14530-pm.png

putHDFS processor

configure the Hadoop Core-site.xml and hdfs-site.xml and destination HDFS directory in this case it is /test-nifi/CDC

Make sure this directory is present in HDFS otherwise create it using the following command

Unix> hadoop fs –mkdir –p /test-nifi/CDC

Make sure all the processors are running in NiFi

7439-screen-shot-2016-09-07-at-33204-pm.png

Testing CDC

Run a bunch of insert statements on MySQL database.

mysql –u test_cdc –p

at the mysql CLI

run the following inserts:

insert into cdc_test values (3, 'cdc3', null, null);

insert into cdc_test values (4, 'cdc3', null, null);

insert into cdc_test values (5, 'cdc3', null, null);

insert into cdc_test values (6, 'cdc3', null, null);

insert into cdc_test values (7, 'cdc3', null, null);

insert into cdc_test values (8, 'cdc3', null, null);

insert into cdc_test values (9, 'cdc3', null, null);

insert into cdc_test values (10, 'cdc3', null, null);

insert into cdc_test values (11, 'cdc3', null, null);

insert into cdc_test values (12, 'cdc3', null, null);

insert into cdc_test values (13, 'cdc3', null, null);

select * from cdc_test

go to hive using cli and check if the records were transferred over using NIFI.

Hive> select * from hive_test_cdc

Voila…

3,210 Views
Comments
Expert Contributor

I had questions about the need for the triggers, The main reason for creating Triggers in mysql are

1) Triggers set up date and time stamp whenever a row is inserted or updated and NIFI processor is polling on the date and time column to pull the latest data from RDBMS into nifi to generate a flow file. Date and time field is critical.

2) Also, it helps to figure out if the record was inserted or updated in Mysql as well as in Hive. So we know the state of the record in the source system. This field is just being used for demo purpose, its not really required to set this data.

New Contributor

Hi! I tried to use this setup for MariaDB - without success... i.e. my trial already failed at the CDC-Processor (with a dockerized NiFi and the org.mariadb.jdbc.Driver). Is MariaDB known to not work?

PS: without the Distributed-Map-Cache-Client - it works (of course I don't get the table and column names - which I guess would be "more than just nice"... with the DMCC I get a JDBC error "creating binlog enrichment"

Don't have an account?
Coming from Hortonworks? Activate your account here
Version history
Revision #:
2 of 2
Last update:
‎08-17-2019 10:15 AM
Updated by:
 
Contributors
Top Kudoed Authors