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Objective

This tutorial is the second article of a three part series. We will walk-through a Apache NiFi CDC flow which uses MySQL bin logs to create a copy of a table and keep the copy in sync with row-level changes to the source. The last article in the series will delve into the finer details of the flow configuration, suggest best practices and highlight potential trouble spots.

Environment

This tutorial was tested using the following environment and components:

  • Mac OS X 10.11.6
  • MySQL 5.7.13
  • Apache NiFi 1.3.0

NiFI CDC Flow Walk Through

Prerequisites

20421-1-cdc-flow.png

  • Your MySQL instance (with binary logging enabled) is running. A 'users' table exists in your "source" database. Your "copy" database is empty.
  • All controller services are enabled.

Flow Overview

Here is a quick overview of the CDC flow:

1. CaptureChangeMySQL reads the bin logs to generate FlowFiles (JSON)

2. FlowFiles are routed based on event type:

  • Begin/Commit events: JSON manipulated by JoltTransformJSON
  • DDL events: schema (QUERY) and statement type (SQL) attributes are added
  • Delete/Insert/Update events: table name, schema (USERS) and statement type attributes are added, JSON manipulated

3. EnforceOrder ensures all change events are processed in the correct order

4. PutDatabaseRecord uses a RecordReader to input multiple records from the incoming flow files. These records are translated to SQL statements and executed as a single batch.

Flow Details

Looking at the flow in detail:

CaptureChangeMySQL Processor

Select the first processor in the flow, CaptureChangeMySQL. Right-click to see the context menu and select "Configuration" to view the Configure Processor window. Select the "Properties" tab.

20485-2-capturechangemysql-properties.png

MySQL Hosts, MySQL Driver Class Name, MySQL Driver Location(s), Username, and Password are configured to point to the "source" MySQL database.

"Server ID" is not specified, which defaults the value to 65535. It should not match the server_id in the my.cnf file that we configured in the first article of this tutorial series.

"Distributed Map Cache Client" is set to the DistributedMapCache controller service "CDC MapCache" to store state information and keep it up to date.

"Include Begin/Commit" Events and "Include DDL Events" are set to "true" for completeness, to demonstrate how the CaptureChangeMySql processor can handle events in the bin log in addition to Delete/Insert/Update events. The DDL events are also needed to ultimately generate the SQL for the `users` table creation in the "copy" database.

Close the Configuration Window. With the processor still highlighted, right-click to see the context menu and select "Start" to run this single processor. 13 FlowFiles should be generated.

20423-3-capturechangemysql-start.png

The 13 flowfiles are for the 13 events in the bin log: 1 DDL event for the creation of the 'users' table, 1 begin event, 10 insert events for the rows added to the table, and 1 commit event. The contents of these flowfiles can be seen if you right-click on the connection where the 13 flowfiles are queued and select "List queue". Select the View Details button ("i" icon) next to any row to see the details and attributes:

20424-4-5-cdc-details-attributes.png

Selecting the "VIEW" button on the Details tab displays the contents of the flowfile. Here are the contents of the DDL event flowfile:

20425-6-ddl-event-contents.png

RouteOnAttribute Processor

The next processor in the flow is RouteOnAttribute. Looking at the properties:

20426-7-routeonattribute-properties.png

this processor routes the flowfiles depending on the event type. Run this processor and we see the expected results of 10 insert event flowfiles sent to the "delete, insert, update" connection, 1 ddl event flowfile sent to the "ddl" connection and 2 total flowfiles (1 begin event, 1 commit event) sent to the "begin, commit" connection.

20427-8-routeonattribute-start.png

At this point, the flow has multiple branches. Let's look at the BEGIN/COMMIT and DDL paths of the flow first.

Begin/Commit Path

The begin/commit flowfiles are sent to a JoltTransformJSON processor which uses a Shift Jolt transformation DSL to put the begin/commit events in the "query" field of the JSON:

20428-9-jolttransformjson-properties.png

Here is an example of the JSON from the incoming begin event flowfile:

{
  "type" : "begin",
  "timestamp" : 1499702324000,
  "binlog_filename" : "delta.000001",
  "binlog_position" : 1070,
  "database" : "source"
}

Then after running the processor:

20429-10-jolttransformjson-start.png

here is the flattened result:

{"query":"begin"}

DDL Path

For the DDL path, the contents of the DDL flowfile already has a "query" field, so no JSON transformation is needed:

{
  "type" : "ddl",
  "timestamp" : 1499701819000,
  "binlog_filename" : "delta.000001",
  "binlog_position" : 384,
  "database" : "source",
  "table_name" : null,
  "table_id" : null,
  "query" : "create table `users` (\n `id` mediumint(9) not null auto_increment primary key,\n `title` text,\n `first` text,\n `last` text,\n `street` text,\n `city` text,\n `state` text,\n `zip` text,\n `gender` text,\n `email` text,\n `username` text,\n `password` text,\n `phone` text,\n `cell` text,\n `ssn` text,\n `date_of_birth` timestamp null default null,\n `reg_date` timestamp null default null,\n `large` text,\n `medium` text,\n `thumbnail` text,\n `version` text,\n `nationality` text\n) engine=innodb auto_increment=1 default charset=latin1"
}

Schema=query & StmtType=SQL (UpdateAttribute Processor)

The begin/commit and ddl flowfiles are now both sent to a UpdateAttribute processor which adds the schema name and statement type attributes with the values of "query" and "SQL" respectively.

20430-11-schema-query-statement-type-properties.png

After starting the processor:

20431-12-schema-query-statement-type-start.png

Here is an example of these attributes added to the flowfile:

20432-13-schemaname-statementtype-attributes.png

Delete, Insert, Update Path

Now let's look at the DELETE/INSERT/UPDATE path of the flow.

Get Table Name (EvaluateJsonPath Processor)

This processor adds the attribute tableName to each of the flowfiles:

20433-14-gettablename-properties.png

with a value of "users" from the flowfile contents via expression language.

After starting the processor:

20434-15-gettablename-start.png

here is an example of the new tableName attribute and value added to one of the flowfiles:

20435-16-tablename-attribute.png

Transform to Flat JSON (JoltTransformJSON Processor)

The next processor, JoltTransformJSON, simplifies and formats the JSON in the flowfiles in order for these insert SQL statements to be applied to the `users` table in the copy db (applied by the PutDBRecord processor later in the flow). Looking at the configuration for this processor:

20437-17-transformtoflatjson-properties.png

As shown, a Chain Jolt transformation DSL is used in conjunction with a Jolt "shift" specification to perform the flattening.

Here is an example of the JSON from an incoming flowfile:

{
  "type" : "insert",
  "timestamp" : 1499702324000,
  "binlog_filename" : "delta.000001",
  "binlog_position" : 1246,
  "database" : "source",
  "table_name" : "users",
  "table_id" : 108,
  "columns" : [ {
    "id" : 1,
    "name" : "id",
    "column_type" : 4,
    "value" : 1
  }, {
    "id" : 2,
    "name" : "title",
    "column_type" : -1,
    "value" : "miss"
  }, {
    "id" : 3,
    "name" : "first",
    "column_type" : -1,
    "value" : "marlene"
  }, {
    "id" : 4,
    "name" : "last",
    "column_type" : -1,
    "value" : "shaw"
  }, {
    "id" : 5,
    "name" : "street",
    "column_type" : -1,
    "value" : "3450 w belt line rd"
  }, {
    "id" : 6,
    "name" : "city",
    "column_type" : -1,
    "value" : "abilene"
  }, {
    "id" : 7,
    "name" : "state",
    "column_type" : -1,
    "value" : "florida"
  }, {
    "id" : 8,
    "name" : "zip",
    "column_type" : -1,
    "value" : "31995"
  }, {
    "id" : 9,
    "name" : "gender",
    "column_type" : -1,
    "value" : "F"
  }, {
    "id" : 10,
    "name" : "email",
    "column_type" : -1,
    "value" : "marlene.shaw75@example.com"
  }, {
    "id" : 11,
    "name" : "username",
    "column_type" : -1,
    "value" : "goldenpanda70"
  }, {
    "id" : 12,
    "name" : "password",
    "column_type" : -1,
    "value" : "naughty"
  }, {
    "id" : 13,
    "name" : "phone",
    "column_type" : -1,
    "value" : "(176)-908-6931"
  }, {
    "id" : 14,
    "name" : "cell",
    "column_type" : -1,
    "value" : "(711)-565-2194"
  }, {
    "id" : 15,
    "name" : "ssn",
    "column_type" : -1,
    "value" : "800-71-1872"
  }, {
    "id" : 16,
    "name" : "date_of_birth",
    "column_type" : 93,
    "value" : "1991-10-07 00:22:53.0"
  }, {
    "id" : 17,
    "name" : "reg_date",
    "column_type" : 93,
    "value" : "2004-01-29 16:19:10.0"
  }, {
    "id" : 18,
    "name" : "large",
    "column_type" : -1,
    "value" : "http://api.randomuser.me/portraits/women/67.jpg"
  }, {
    "id" : 19,
    "name" : "medium",
    "column_type" : -1,
    "value" : "http://api.randomuser.me/portraits/med/women/67.jpg"
  }, {
    "id" : 20,
    "name" : "thumbnail",
    "column_type" : -1,
    "value" : "http://api.randomuser.me/portraits/thumb/women/67.jpg"
  }, {
    "id" : 21,
    "name" : "version",
    "column_type" : -1,
    "value" : "0.6"
  }, {
    "id" : 22,
    "name" : "nationality",
    "column_type" : -1,
    "value" : "US"
  } ]
}

Then after running the processor:

20439-18-transformtoflatjson-start.png

here is the flattened result:

[ {
  "id" : 1,
  "title" : "miss",
  "first" : "marlene",
  "last" : "shaw",
  "street" : "3450 w belt line rd",
  "city" : "abilene",
  "state" : "florida",
  "zip" : "31995",
  "gender" : "F",
  "email" : "marlene.shaw75@example.com",
  "username" : "goldenpanda70",
  "password" : "naughty",
  "phone" : "(176)-908-6931",
  "cell" : "(711)-565-2194",
  "ssn" : "800-71-1872",
  "date_of_birth" : "1991-10-07 00:22:53.0",
  "reg_date" : "2004-01-29 16:19:10.0",
  "large" : "http://api.randomuser.me/portraits/women/67.jpg",
  "medium" : "http://api.randomuser.me/portraits/med/women/67.jpg",
  "thumbnail" : "http://api.randomuser.me/portraits/thumb/women/67.jpg",
  "version" : "0.6",
  "nationality" : "US"
} ]

Schema=users & Statement Type (UpdateAttribute Processor)

The next step in the flow is an UpdateAttribute processor which adds the schema name and statement type attributes to the flowfiles.

20440-19-schema-users-statement-type-properties.png

After starting the processor:

20441-20-schema-users-statement-type-start.png

Here is an example of these attributes added to one of the insert flowfiles:

20443-21-schemaname-statementtype-attributes.png

EnforceOrder Processor

The two flow paths converge at an EnforceOrder processor:

20444-22-convergence.png

This processor guarantees order delivery of the CDC events based on sequence id, which were generated by the CaptureChangeMySQL processor at the beginning of the flow (cdc.sequence.id attribute).

20445-23-enforceorder-properties.png

The connection that follows EnforceOrder, is configured to prioritize flowfiles by "first in, first out":

20446-24-firstinfirstoutprioritizer.png

Running the processor results in the following:

20447-25-enforceorder-start.png

Note: While the number of files that are queued after the processor is 13 as expected, 24 total flowfiles were processed In/Out. This is because some flowfiles went through the "wait" connection. This is confirmed if you right-click on the wait connection and select "Status History":

20448-26-wait-connection-status-history.png

PutDatabaseRecord Processor

With the order of the CDC events ensured, the next and final processor is PutDatabaseRecord. Looking at it's configuration:

20449-27-putdatabaserecord-properties.png

the Record Reader property points to the "JsonPathReader" controller service, which parses the incoming data and determines the data's schema (more on this later). Statement Type property specifies the type of SQL statement to generate. In this flow it is set to "Use statement.type Attribute", which is necessary for the flow to handle more than individual INSERT, UPDATE, DELETE types. In conjunction with the Field Containing SQL property set to "query", the processor: 1) looks at the statement.type attribute from each Delete/Insert/Update flowfile to apply the appropriate delete/insert/update SQL and 2) assumes the value of the "query" field is valid SQL and applies it as-is for the Begin/Commit/DDL flow files. Table Name property is set to the "tableName" attribute via Expression Language, which is "user" for the flowfiles. Database Connection Pooling Service is set to the MYSQL CDC Backup controller service. This DBCPConnectionPool controller service points to the target “copy” database:

20450-28-mysqlcdcbackup-properties.png

JsonPathReader Record Reader

As mentioned earlier, the Record Reader used in the processor is the "JsonPathReader" controller service. JsonPathReader dynamically reads JSON files that have any schema. The reader specifies the schema expected in an attribute, which in this flow is schema.name.

20451-29-jsonpathreader-properties.png

Schema Registry property is set to the AvroSchemaRegistry controller service. AvroSchemaRegistry which defines the "query" and "users" schemas.

20452-30-31-avroschemaregistry-query-users.png

Note: For more information on Record Readers/Writers, see https://community.hortonworks.com/content/kbentry/106450/record-oriented-data-with-nifi.html.

Starting the PutDatabaseRecord processor should process 13 flowfiles going to Success.

20454-32-33-putdatabaserecord-start-copy-users-table.png

As a result, a `user` table now exists in the "copy" database which is equivalent to the original `user` table in the "source" database.

Table Synchronization

With all of the processors in the flow running (except for the LogAttribute ones), any row-level changes to the original `users` table in the source database will be applied in real-time to the `users` table in the copy database.

Delete, add or modify some rows and you will see these change events processed by the flow to keep the tables in sync.

Review

This tutorial walked you through a sample NiFi CDC flow, examining each component in the flow in detail including the critical processors CaptureChangeMySQL, EnforceOrder and PutDatabaseRecord. Running the flow, created a `user` table in the copy database that is identical to the original `user` table in the source database. With these processors in the flow running, any changes in the original `user` table are also applied to the replicated `user` table. Continue to the third article in this tutorial series to delve into more details of the flow configuration and learn about best practices and potential trouble spots.

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Comments
New Contributor

Why there are NULL database name and table name in delete/update/create output of capture processor of mine but normal in begin/commit event type? Anything wrongly configured?

{"type":"insert","timestamp":1507709276000,"binlog_filename":"mysql-bin.000658","binlog_position":93481655,"database":null,"table_name":null,"table_id":null,"columns":[{"id":1,"value":10},{"id":2,"value":"mrs"},{"id":3,"value":"erika"},{"id":4,"value":"king"},{"id":5,"value":"1171 depaul dr"},{"id":6,"value":"addison"},{"id":7,"value":"wisconsin"},{"id":8,"value":"50082"},{"id":9,"value":"F"},{"id":10,"value":"erika.king55@example.com"},{"id":11,"value":"goldenbutterfly498"},{"id":12,"value":"chill"},{"id":13,"value":"(635)-117-5424"},{"id":14,"value":"(662)-110-8448"},{"id":15,"value":"122-71-7145"},{"id":16,"value":null},{"id":17,"value":null},{"id":18,"value":"http://api.randomuser.me/portraits/women/52.jpg"},{"id":19,"value":"http://api.randomuser.me/portraits/med/women/52.jpg"},{"id":20,"value":"http://api.randomuser.me/portraits/thumb/women/52.jpg"},{"id":21,"value":"0.6"},{"id":22,"value":"US"}]}

{"type":"commit","timestamp":1507689471000,"binlog_filename":"mysql-bin.000657","binlog_position":21750290,"database":"mercury_dev"}

Guru

Hi @Casel Chen,

Just to confirm: Did you use a Distributed Map Cache Client/Server as discussed in the first article? There is a Jira that is possibly related to what you are seeing if not: https://issues.apache.org/jira/browse/NIFI-3902

Also, are you using a MySQL? Some issues have been reported if using MariaDB.

Thanks!

New Contributor

Hi @Andrew Lim,

No, I didn't use Distributed Map Cache Client/Server.
Yes, I use MySQL 5.6.

I also wondered how to replicate MySQL Data to other None MySQL DB, like Hive or HBase, can we still use PutDatabaseRecord processor? How to handle 'Delete' action? Thanks!

Guru

@Casel Chen,

Thanks for your response. Hoping your original issue is resolved if you setup the Distributed Map Cache Server as detailed in the first article of this tutorial. My flow template (attached with the tutorial) has the Distributed Map Cache Client controller service.

PutDatabaseRecord does not support Hive or HBase. For Hive, use a PutHiveStreaming processor instead. PutHiveStreaming expects Avro format.  You can use the ConvertRecord processor to convert to Avro.

New Contributor

@Andrew Lim
Question regarding the AvroSchemaRegistry -

You stated > AvroSchemaRegistry which defines the "query" and "users" schemas.

Does this mean that it creates the schemas by itself? or do the schemas have to be created manually? and if they have to be created manually, how does that work with the DDL scripts beings passed? Does the schema have to be updated manually each time there's a DDL change?

Thank you for the tutorial! I'm excited to jump in and see if I can get this working on my end.

Guru

Hi @K Henrie

You define the schemas based on the expected data that is being processed.

If I am understand your questions, no, the "query" schema does not need to be updated manually. It should handle all the Begin/Commit/DDL flow files.

Not applicable

Hi @Andrew Lim, great job with the tutorial. I have managed to set up my flow and get captures of the begin/commit events as well as the delete/insert/update events, after I update my original table by removing a few rows. However, I am not getting any ddl events through after the CaptureChangeMySQL processor, which means I don't get a "users" table in the "copy" database with the original data. As I understand this copy.users table is supposed to be automatically created with the ddl events being processed? My "include DDL events" are set to true.

Any ideas?

Best regards,

Emil

Guru

Hi @Emil Brännström

Thanks for your comments. I hope we can get the flow working for you end-to-end.

The copy.users table should be automatically created, assuming you are capturing all the ddl events needed for it (the 1 DDL event for the creation of the 'users' table, 1 begin event, X # of insert events for the rows added to the table, and 1 commit event).

What are the flowfile contents after CaptureChangeMySQL?

It might also be helpful to check some of the troubleshooting tips in the third article, especially the ones regarding clearing state.

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