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Displaying posts with tag: slave (reset)
RDS Aurora MySQL and Service Interruptions

In Amazon space, any EC2 or Service instance can “disappear” at any time.  Depending on which service is affected, the service will be automatically restarted.  In EC2 you can choose whether an interrupted instance will be restarted, or left shutdown.

For an Aurora instance, an interrupted instance is always restarted. Makes sense.

The restart timing, and other consequences during the process, are noted in our post on Aurora Failovers.

Aurora Testing Limitations

As mentioned earlier, we love testing “uncontrolled” failovers.  That is, we want to be able to pull any plug on any service, and see that the environment as a whole continues to do its job.  We can’t do that with Aurora, because we can’t control the essentials:

  • power button;
  • reset switch;
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RDS Aurora MySQL Failover

Right now Aurora only allows a single master, with up to 15 read-only replicas.

Master/Replica Failover

We love testing failure scenarios, however our options for such tests with Aurora are limited (we might get back to that later).  Anyhow, we told the system, through the RDS Aurora dashboard, to do a failover. These were our observations:

Role Change Method

Both master and replica instances are actually restarted (the MySQL uptime resets to 0).

This is quite unusual these days, we can do a fully controlled role change in classic asynchronous replication without a restart (CHANGE MASTER TO …), and Galera doesn’t have read/write roles as such (all instances are technically writers) so it doesn’t need role changes at all.

Failover Timing

Failover between running instances takes about 30 seconds.  This is in line with information provided in the …

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Exploring Amazon RDS Aurora: replica writes and cache chilling

Our clients operate on a variety of platforms, and RDS (Amazon Relational Database Service) Aurora has received quite a bit of attention in recent times. On behalf of our clients, we look beyond the marketing, and see what the technical architecture actually delivers.  We will address specific topics in individual posts, this time checking out what the Aurora architecture means for write and caching behaviour (and thus performance).

What is RDS Aurora?

First of all, let’s declare the baseline.  MySQL Aurora is not a completely new RDBMS. It comprises a set of Amazon modifications on top of stock Oracle MySQL 5.6 and 5.7, implementing a different replication mechanism and some other changes/additions.  While we have some information (for instance from the “deep dive” by AWS VP Anurag Gupta), the source code of the Aurora modifications …

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Checking if a Slave Has Applied a Transaction from the Master

In this blog post, we will discuss how we can verify if an application transaction executed on the master has been applied to the slaves.

In summary, is a good practice to alleviate the load on the master by doing reads on slaves. It is acceptable in most of the cases to just connect on slaves and issue selects. But there are some cases we need to ensure that the data we just applied on our master has been applied on the slaves before we query it.

One way to do this is using a built-in function called MASTER_POS_WAIT. This function receives a binary log name and position. It will block the query until the slave applies transactions up to that point, or timeout. Here is one example of how to use it:

-- insert our data on master
master [localhost] {msandbox} (test) > INSERT INTO test VALUES …
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Creating An External Slave For A Live AWS Aurora Instance

Overview

When working with Amazon AWS Aurora, there are some steps to consider when trying to get data out of an active Aurora master into a slave, potentially into a EC2 instance or offsite in another data centre. Creating an external mysql to Aurora gives the option to move out of Aurora, or to have the flexibility to move data around as desired. With AWS RDS instances this task is pretty simple because you can do the following :

  1. Create a read replica
  2. Stop the slave process
  3. Capture the positioning
  4. Dump the database

With Aurora it’s a little trickier, because a read replica in Aurora has no slave process. All of the replication is handled on the back end and cannot be controlled. However, setting up an external slave can be done.

Amazon AWS Documentation

In …

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Video on MySQL master slave Replication

A video session on "Intro to MySQL master slave Replication". Hope you enjoy it :)

Docker MySQL Replication 101

In this blog post, we’ll discuss some of the basics regarding Docker MySQL replication. Docker has gained widespread popularity in recent years as a lightweight alternative to virtualization. It is ideal for building virtual development and testing environments. The solution is flexible and seamlessly integrates with popular CI tools.

 

This post walks through the setup of MySQL replication with Docker using Percona Server 5.6 images. To keep things simple we’ll configure a pair of instances and override only the most important variables for replication. You can add whatever other variables you want to override in the configuration files for each instance.

Note: the configuration described here is suitable for development or testing. We’ve also used the …

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Fixing inconsistency on MySQL Slave of Galera Cluster

This blog post explores the syncing options for an inconsistent MySQL slave of Galera cluster node using pt-table-sync

Syncing Inconsistent MySQL Slaves

 

Checksum is a standard practice among DBAs to verify the data consistency across replicated nodes. In this post we’re going to review the syncing options for an inconsistent MySQL slave of Galera cluster node.

Here we’re assuming a setup of regular replication to a MySQL instance from one of the Galera cluster nodes.

In the usual MySQL replication setup, standard practice involves the usage of the pt-table-checksum tool to identify the discrepancies and usage of pt-table-sync to bring them in sync. The checksum tool, pt-table-checksum, can run across Galera cluster node to verify the data consistency and confirm if the MySQL slave is consistent with a chosen primary node.

What happens if this Galera cluster’s regular MySQL slave sees data inconsistency on it? Will pt-table-sync work there? The answer to this depends…
pt-table-sync when used with –sync-to-master …

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Log Buffer #429: A Carnival of the Vanities for DBAs

This Log Buffer Edition gathers a wide sample of blogs and then purifies the best ones from Oracle, SQL Server and MySQL.

Oracle:

  • If you take a look at the “alter user” command in the old 9i documentation, you’ll see this: DEFAULT ROLE Clause.
  • There’s been an interesting recent discussion on the OTN Database forum regarding “Index blank blocks after a large update that was rolled back.”
  • 12c Parallel Execution New Features: 1 SLAVE distribution
  • Index Tree Dumps in Oracle 12c …
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