Configure Parallel Replication with MariaDB Xpand

Overview

MariaDB Xpand 6 provides parallel replication for applications that require extremely scalable replication between Xpand clusters:

  • Parallel replication minimizes latency and slave lag

  • Multiple Xpand nodes stream and apply events independently in parallel

  • Xpand ensures transactional consistency and commits transactions in the same order as the replication primary

  • Parallel replication can only be used when replicating from another MariaDB Xpand cluster

  • Parallel replication is supported with MariaDB Xpand 6

  • Xpand requires row-based replication (RBR) for parallel replication

  • For parallel replication, all replicated tables should have primary keys

This page explains how to configure parallel replication with MariaDB Xpand. Before configuring parallel replication, ensure that the special cases for replication and special cases for parallel replication do not apply to your environment.

For information on the architecture related to parallel replication with MariaDB Xpand, see "MariaDB Xpand Parallel Replication Architecture".

Compatibility

  • MariaDB Xpand 6

Configure Binlogs on Master for Parallel Replication

Configure binlogs on the master by executing CREATE BINLOG .. FORMAT='ROW':

CREATE BINLOG 'binlog_name'
   [LOG (target1, target2, ...),]
   [IGNORE (target3, target4, ...),]
   FORMAT='ROW';

For additional information, see "Configure MariaDB Xpand as a Replication Master".

Configure Parallel Replication on Slave

Configure parallel replication by executing CREATE SLAVE:

CREATE SLAVE slave_name PARALLEL_LOG = master_log_name, PARALLEL_POS = position, SLICES = num_slices, BATCH_SIZE_MS = batch_size
          [, MASTER_HOST = master_host]
          [, MASTER_USER = master_user]
          [, MASTER_PASSWORD =  master_password]
          [, MASTER_PORT = master_port];

Parallel Replication Specific Options

PARALLEL_LOG

This is used in place of MASTER_LOG_FILE when configuring Parallel Replication. Unlike MASTER_LOG_FILE, PARALLEL_LOG does not require the file number, only the name of the binlog.

For example: if your binlog file is binlog-bin.000001, the PARALLEL_LOG is binlog-bin.

PARALLEL_POS

This replaces the file based replication argument MASTER_LOG_POS. This value can be found by running SHOW MASTER STATUS PARALLEL or extracted from the metadata of the backup file if restoring from backup. If restoring from backup for the purposes of replication, the value in the backup should be used with "0x" prepended to the value.

For example: if the value from your backup file is 5e23e65e9342f802 then your PARALLEL_POS is 0x5e23e65e9342f802.

SLICES

Determines the amount of parallel threads the slave will connect to the master with. This value should be N or N*2, where N is the number of nodes in the master cluster. If your cluster contains 6 nodes then the value for SLICES would be 6, or 12.

BATCH_SIZE_MS

The amount of time in milliseconds used to determine transactions batch size on the master. Default of 3000 ms.

Since the master uses time to batch transactions, the data on the slave may show 0 seconds behind master, but the actual data will be between 0 and BATCH_SIZE_MS. You can reduce this latency by setting BATCH_SIZE_MS lower, such as to 1000ms or even 500ms, however this can decrease replication performance dependent on workload.

Note

For optimal performance MASTER_HOST should point to the master cluster's load balancer.

Using the Values in Backup to Configure Parallel Replication

When restoring from a backup for the purposes of replication you can find the values to set PARALLEL_LOG and PARALLEL_POS in the binlogs and xid files. The two files are located inside the metadata directory of the Xpand backup directory.

Note

Please note that the value in the xid file appears in hexadecimal but without an 0x prefix. When setting PARALLEL_POS with a hexadecimal value, it must start with 0x .

[root@server01]# cat backup_all-2020-01-10/metadata/binlogs
binlog01.001662:18570355
[root@server01]# cat backup-2020-01-10/metadata/xid
5e23e65e9342f802

Using the above output, the values to use for PARALLEL_LOG and PARALLEL_POS would be binlog01 and 0x5e23e65e9342f802 respectively.

The command using the values from the output above as an example would be:

CHANGE SLAVE slave_name TO PARALLEL_LOG='binlog01', PARALLEL_POS='0x5e23e65e9342f802';

Viewing Parallel Replication Status:

To display the status of a parallel master:

SHOW MASTER STATUS PARALLEL;
SHOW ALL MASTER STATUS PARALLEL;

Displaying the status of a parallel slave is the same as with a serial slave:

SHOW SLAVE STATUS slave_name;
SHOW SLAVE STATUS;

To view additional information about the Parallel slave, such as the value of SLICES or BATCH_SIZE_MS, use the table system.mysql_repconfig:

SELECT * FROM system.mysql_repconfig WHERE slave_name = 'slave_name';
SELECT slave_name, protocol, slices, batch_size / POW(2, 32) * 1000 AS batch_size_ms
FROM system.mysql_repconfig WHERE slave_name = 'slave_name';

How it Works

The Xpand Parallel slave is able to parallelize processing of the replication stream and applies events in batches. Row events from within the same transaction are applied in the same transaction on the slave. Both serial and parallel replication use the same Replication Master for generating binlog(s).

Special Cases

Slave Xpand Cluster

MariaDB Xpand's parallel replication can only be used with a slave Xpand cluster.

Row-Based Replication

MariaDB Xpand requires row-based replication (RBR) for parallel replication, so the binary log should not be created in the statement-based replication (SBR) format.

On the primary Xpand cluster, the binary log can be created in the row-based replication (RBR) format using CREATE BINLOG .. FORMAT='ROW'.

Primary Keys

Since MariaDB Xpand's parallel replication requires row-based replication (RBR), all replicated tables should have a Primary Key.

For row-based replication, Xpand uses the table's Primary Key to find the specific row referenced in each binlog event. If any tables do not have a Primary Key, Xpand must scan the table for the row, which can have a negative impact on performance.

Foreign Keys

MariaDB Xpand does not support foreign keys with parallel replication.

Primary Keys and Unique Indexes

In many cases when a table has both a Primary Key and a Unique index, Xpand can force the table to use serial replication instead of parallel replication.

When using Xpand's parallel replication, MariaDB does not recommend creating tables that have both a Primary Key and a Unique index.