Your question: What causes MySQL replication lag?

Replication lag is caused when either the I/O Thread or SQL Thread cannot cope with the demands placed upon it. If the I/O Thread is suffering, this means that the network connection between the master and its slaves is slow. … There may be long-running transactions or too much I/O activity.

How do I fix MySQL replication lag?

To minimize slave SQL_THREAD lag, focus on query optimization. My recommendation is to enable the configuration option log_slow_slave_statements so that the queries executed by slave that take more than long_query_time will be logged to the slow log.

Why does replication lag?

Replication lag occurs when the slaves cannot keep up with the updates occurring on the master. Unapplied changes accumulate in the slave’s relay logs and the version of the database on the slaves becomes increasingly different from that of the master.

How do you reduce latency in replication?

This is an expected delay, but you can minimize this lag by monitoring the slow query log on the primary instance. You can also identify long-running statements to reduce lag. Then, break long-running statements into smaller statements or transactions.

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How do I monitor MySQL replication?

Replication is best monitored by checking the following variables:

  1. SLAVE_RUNNING: This is a global status variable and its value can be checked using SHOW GLOBAL STATUS like ‘slave_running’. …
  2. If slave_running is ‘ON’, then the slave is up and working fine, which means both the SQL thread and the IO thread are running.

How does MySQL replication work?

The MySQL replication feature allows a server – the master – to send all changes to another server – the slave – and the slave tries to apply all changes to keep up-to-date with the master. … The master has a thread, called the dump thread, that continuously reads the master’s binlog and sends it to the slave.

What is replication latency?

Replication latency is the amount of time it takes for a transaction that occurs in the primary database to be applied to the replicate database. The time includes Replication Agent processing, Replication Server processing, and network usage.

Does replication improve reliability?

Replication is the key factor in improving the availability of data in distributed information systems. … The scheme increases the reliability as well as the degree of concurrency of the system. A token is used to designate a read-write copy.

Where is replication lag in Mongodb?

To check the current length of replication lag: In a mongosh session that is connected to the primary, call the rs. printSecondaryReplicationInfo() method. A delayed member may show as 0 seconds behind the primary when the inactivity period on the primary is greater than the members[n].

How can I make my replication faster?

Server and Network

  1. Set the minimum and maximum amount of memory allocated to Microsoft SQL Server Database Engine. …
  2. Ensure proper allocation of database data files and log files. …
  3. Consider adding memory to servers used in replication, particularly the Distributor.
  4. Use multiprocessor computers. …
  5. Use a fast network.
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What is Innodb_log_file_size?

innodb_log_file_size is the size of a log file (in bytes). There exist multiple log file for MySQL to write the data to. This particular system-variable tells the file size of one of such log files.

What is parallel replication?

Parallel replication is a much-expected feature of MySQL. … In MySQL 5.5 and MariaDB 5.5, replication is single threaded: on a slave, the previous transaction must complete (commit) before the next transaction can start. This is not the case on a master where many transactions can make progress at the same time.

Does replication affect latency?

Benefits of data replication

Improved network performance: Having the same data in multiple locations can lower data access latency, since required data can be retrieved closer to where the transaction is executing.

How does MongoDB reduce replication lag?

Make sure to use all of your tools at your disposal when minimizing MongoDB replication lag. Since the Opslogs has limited space, you won’t want to let it fall too far behind, or else the secondary node can’t catch up with the primary, and if this occurs, you will need to run a full sync.

How do I check my RDS replication status?

In addition to the option to connect to your Read Replica and run the Show Slave Status command to review the replication status, you can now view the replication status of your Read Replicas by simply looking at the “Replication State” field on the DB Instances page of the AWS Management Console.

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