The Ultimate Guide to High Availability with MariaDB

Avrorouter Tutorial

Avrorouter Tutorial

This tutorial is a short introduction to the Avrorouter, how to set it up and how it interacts with the binlogrouter.

The first part configures the services and sets them up for the binary log to Avro file conversion. The second part of this tutorial uses the client listener interface for the avrorouter and shows how to communicate with the the service over the network.

Configuration

Preparing the master server

The master server where we will be replicating from needs to have binary logging enabled, binlog_format set to row and binlog_row_image set to full. These can be enabled by adding the two following lines to the my.cnf file of the master.

binlog_format=row
binlog_row_image=full

You can find out more about replication formats from the MariaDB Knowledge Base

Configuring MaxScale

We start by adding two new services into the configuration file. The first service is the binlogrouter service which will read the binary logs from the master server. The second service will read the binlogs as they are streamed from the master and convert them into Avro format files.

# The Replication Proxy service
[replication-service]
type=service
router=binlogrouter
server_id=4000
master_id=3000
filestem=binlog
user=maxuser
password=maxpwd

# The Avro conversion service
[avro-service]
type=service
router=avrorouter
source=replication-service
filestem=binlog
start_index=15

# The listener for the replication-service
[replication-listener]
type=listener
service=replication-service
protocol=MariaDBClient
port=3306

# The client listener for the avro-service
[avro-listener]
type=listener
service=avro-service
protocol=CDC
port=4001

# The MaxAdmin service and listener for MaxScale administration
[CLI]
type=service
router=cli

[CLI-Listener]
type=listener
service=CLI
protocol=maxscaled
socket=default

The source parameter in the avro-service points to the replication-service we defined before. This service will be the data source for the avrorouter. The filestem is the prefix in the binlog files and start_index is the binlog number to start from. With these parameters, the avrorouter will start reading events from binlog binlog.000015.

Note that the filestem and start_index must point to the file that is the first binlog that the binlogrouter will replicate. For example, if the first file you are replicating is my-binlog-file.001234, set the parameters to filestem=my-binlog-file and start_index=1234.

For more information on the avrorouter options, read the Avrorouter Documentation.

Preparing the data in the master server

Before starting the MaxScale process, we need to make sure that the binary logs of the master server contain the DDL statements that define the table layouts. What this means is that the CREATE TABLE statements need to be in the binary logs before the conversion process is started.

If the binary logs contain data modification events for tables that aren't created in the binary logs, the Avro schema of the table needs to be manually created. There are multiple ways to do this:

  • Dump the database to a slave, configure it to replicate from the master and point MaxScale to this slave (this is the recommended method as it requires no extra steps)

  • Use the cdc_schema Go utility and copy the generated .avsc files to the avrodir

  • Use the Python version of the schema generator and copy the generated .avsc files to the avrodir

If you used the schema generator scripts, all Avro schema files for tables that are not created in the binary logs need to be in the location pointed to by the avrodir parameter. The files use the following naming: <database>.<table>.<schema_version>.avsc. For example, the schema file name of the test.t1 table would be test.t1.0000001.avsc.

Starting MariaDB MaxScale

The next step is to start MariaDB MaxScale and set up the binlogrouter. We do that by connecting to the MySQL listener of the replication_router service and executing a few commands.

CHANGE MASTER TO MASTER_HOST='172.18.0.1',
       MASTER_PORT=3000,
       MASTER_LOG_FILE='binlog.000015',
       MASTER_LOG_POS=4,
       MASTER_USER='maxuser',
       MASTER_PASSWORD='maxpwd';

START SLAVE;

NOTE: GTID replication is not currently supported and file-and-position replication must be used.

This will start the replication of binary logs from the master server at 172.18.0.1 listening on port 3000. The first file that the binlogrouter replicates is binlog.000015. This is the same file that was configured as the starting file in the avrorouter.

For more details about the SQL commands, refer to the Binlogrouter documentation.

After the binary log streaming has started, the avrorouter will automatically start processing the binlogs.

Creating and Processing Data

Next, create a simple test table and populated it with some data by executing the following statements.

CREATE TABLE test.t1 (id INT);
INSERT INTO test.t1 VALUES (1), (2), (3), (4), (5), (6), (7), (8), (9), (10);

To use the cdc.py command line client to connect to the CDC service, we must first create a user. This can be done via maxadmin by executing the following command.

maxadmin call command cdc add_user avro-service maxuser maxpwd

This will create the maxuser:maxpwd credentials which can then be used to request a JSON data stream of the test.t1 table that was created earlier.

cdc.py -u maxuser -p maxpwd -h 127.0.0.1 -P 4001 test.t1

The output is a stream of JSON events describing the changes done to the database.

{"namespace": "MaxScaleChangeDataSchema.avro", "type": "record", "name": "ChangeRecord", "fields": [{"name": "domain", "type": "int"}, {"name": "server_id", "type": "int"}, {"name": "sequence", "type": "int"}, {"name": "event_number", "type": "int"}, {"name": "timestamp", "type": "int"}, {"name": "event_type", "type": {"type": "enum", "name": "EVENT_TYPES", "symbols": ["insert", "update_before", "update_after", "delete"]}}, {"name": "id", "type": "int", "real_type": "int", "length": -1}]}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 1, "timestamp": 1537429419, "event_type": "insert", "id": 1}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 2, "timestamp": 1537429419, "event_type": "insert", "id": 2}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 3, "timestamp": 1537429419, "event_type": "insert", "id": 3}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 4, "timestamp": 1537429419, "event_type": "insert", "id": 4}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 5, "timestamp": 1537429419, "event_type": "insert", "id": 5}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 6, "timestamp": 1537429419, "event_type": "insert", "id": 6}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 7, "timestamp": 1537429419, "event_type": "insert", "id": 7}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 8, "timestamp": 1537429419, "event_type": "insert", "id": 8}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 9, "timestamp": 1537429419, "event_type": "insert", "id": 9}
{"domain": 0, "server_id": 3000, "sequence": 11, "event_number": 10, "timestamp": 1537429419, "event_type": "insert", "id": 10}

The first record is always the JSON format schema for the table describing the types and names of the fields. All records that follow it represent the changes that have happened on the database.

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