Datax Learning notes of

1. brief introduction

Datax It is widely used in Alibaba Group Offline synchronization tool for heterogeneous data sources , Committed to achieving including Relational database （MySQL、Oracle etc. ）、HDFS、Hive、MaxCompute（ primary ODPS）、HBase、FTP etc. Various heterogeneous data sources （ That is, different databases ） Stable and efficient data synchronization between .

1.1 Design concept

​ In order to solve the problem of heterogeneous data source synchronization ,DataX Turn the complex mesh synchronization link into a star data link ,DataX As an intermediate transmission carrier, it is responsible for connecting various data sources . When you need to access a new data source , Just connect this data source pair to DataX, It can achieve seamless data synchronization with existing data sources .

1.2 framework design

DataX As an offline data synchronization framework , use Framework + plugin Architecture building . Abstract data source read and write as Reader/Writer plug-in unit , Integrated into the entire synchronization framework .

• Reader：Reader Data acquisition module , Responsible for collecting data from data sources , Send the data to Framework.

• Writer：Writer Write module for data , To be responsible for keeping up with Framework Take data from , And write the data to the destination .

• Framework：Framework Used to connect to reader and writer, As the data transmission channel of both , And handle buffers , Flow control , Concurrent , Data conversion and other core technical issues .

  DataX 3.0 The open source version supports single machine multithreading mode to complete synchronous job running . Details refer to ： Alicloud open source offline synchronization tool DataX3.0 Introduce

1.3 advantage

1. Reliable data quality monitoring （ So that the data can be transmitted to the destination without damage ）
2. Rich data conversion function
3. Precise speed control
4. The new version DataX3.0 Provided including access （ Concurrent ）、 Record stream 、 Byte stream has three flow control modes , You can control your homework speed at will , Let your work achieve the best synchronization speed within the range that the library can bear .
5. Strong synchronization performance ： Each reading plug-in has one or more segmentation strategies , Can reasonably divide the homework into multiple Task Parallel execution , The single machine multithreaded execution model can make DataX The speed increases linearly with concurrency .
6. Robust fault tolerance mechanism （ Multilevel local / Global retry ）
7. Minimalist experience . Download and use 、 Detailed log information .

1.4 System requirements

• Linux
• JDK（1.8 above , recommend 1.8）
• Python（ recommend Python2.6 X）
• Apache Maven 3.x（Compile DataX）

1.4 build

Official website steps ：https://github.com/alibaba/DataX/blob/master/userGuid.md

2. Relevant concepts

Heterogeneous data sources

​ Refers to data between different database management systems . In the process of enterprise information construction , Due to the phased construction and implementation of data management system in each business system 、 Technical and other economic and human factors , As a result, enterprises have accumulated a large number of business data with different storage methods in the process of development , Including the data management systems used , From simple file database to complex network database , They constitute the heterogeneous data source of the enterprise .

​ The heterogeneity of enterprise data sources is mainly manifested in 3 aspect ：

1. System heterogeneity , That is, the business application system on which the data source depends 、 The differences between database management systems and even operating systems constitute system heterogeneity .
2. Pattern heterogeneity , That is, the data source is different in storage mode . Storage patterns mainly include relational patterns 、 Object mode 、 Object relationship pattern and document nesting , Among them, the relationship mode （ relational database ） It is the mainstream storage mode . meanwhile , Even the same storage mode , There may also be differences in their model structures . For example, the data types of different relational data management systems are not completely consistent , Such as DB2、Oracle、Sybase、Informix、SQL Server、Foxpro etc. .
3. Heterogeneous sources , That is, the heterogeneity between internal data sources and external data sources .

3. DataX3.0 Core architecture

​ DataX Complete the operation of single data passing , We become Job,DataX Received a Job after , A process will be started to complete the job synchronization process .DataX Job The module is the central management node of a single job , Data cleaning 、 Sub task segmentation 、TaskGroup Management and other functions .

• DataX Job After starting , According to the segmentation strategies of different sources , take Job Cut into smaller ones Task （ The subtasks ）, To facilitate concurrent execution .
• next DataX Job Would call Scheduler modular , According to the configured concurrent number , To divide into Task Back together , Assemble into TaskGroup （ Task force ）
• every last Task All by TaskGroup Responsible for starting ,Task After starting , It will start in a fixed way Reader --> Channel --> Writer Thread to complete task synchronization .
• DataX After the job is started ,Job Would be right TaskGroup Conduct monitoring operation , Wait for all TaskGroup After completion ,Job Will be successfully launched （ Abnormal exit Value not 0）

Composition Introduction ：

• Job： The management node of a single job , Responsible for data cleaning 、 Subtask Division 、TashGroup Monitoring management .
• Task： from Job Cut it up , yes DataX The smallest unit of work , Every Task Be responsible for the synchronization of some data .
• Schedule： take Task form TaskGroup, Single TaskGroup The number of concurrent is 5.
• TaskGroup： Responsible for starting Task.

DataX Scheduling process ：

1. First DataX Job The module will be divided into several modules according to the sub database and sub table Task, Then, according to the user configuration, the number of concurrent , To calculate how many... Need to be allocated TaskGroup;
2. The calculation process ：Task / Channel = TaskGroup, Finally by TaskGroup Run according to the allocated concurrency number Task （ Mission ）