Continuing on the series of blog posts about MySQL High Availability, today we will talk about stale reads and how to overcome this issue.

The Problem

Stale reads is a read operation that fetches an incorrect value from a source that has not synchronized an update operation to the value (source Wiktionary).

A practical scenario is when your application applies INSERT or UPDATE data to your master/writer node, and has to read it immediately after. If this particular read is served from another server in the replication/cluster topology, the data is either not there yet (in case of an INSERT) or it still provides the old value (in case of an UPDATE).

If your application or part of your application …

As per the documentation, pt-table-checksum is a tool to perform online replication consistency checks by executing checksum queries on the master, which produces different results on replicas that are inconsistent with the master.

The master and each slave insert checksums into the percona.checksums table, and these are later compared for differences. It’s fairly obvious that the checksums need to be determined independently on each node, and so these inserts must be replicated as STATEMENT and not ROW. Otherwise, the slaves would just insert the same checksum as the master and not calculate it independently.

The tool only requires

binlog_format=STATEMENT

  for its own session. It sets this itself on the master, but will error if this isn’t already set on each slave node. The …

This is Part #2 of the MySQL Master Replication Crash Safety series.  In the previous post, we explored the consequence of reducing durability on masters with slaves using legacy file+position replication.  The consequences are data inconsistencies with a clear warning sign: the slaves stop replicating and report an error.  In this post, we extend our understanding of the impact of running a

“Delayed replication” is one of the important features which were being supported in MySQL from 5.6 for a very long time. This induces an intentional lag in the slave, making it lag by the defined time interval.

For a long time this was not available with the RDS version of MySQL provided by AWS, Recently from the version 5.6.40, 5.722 and later versions this feature is available with all the regions.

I will give a small intro on Amazon RDS, Which is DBAAS provided by Amazon, where you will be given an end-point for all your DB operations and major of admin task of server and DB is taken care by Amazon, To know more you can view our presentation here

In this blog, I will demonstrate, how to have a delayed slave with Amazon RDS for MySQL

Note: If you are …

Quickly Add a Node to an InnoDB Cluster or Group Replication (Shutterstock)

In this blog, we’ll look at how to quickly add a node to an InnoDB Cluster or Group Replication using Percona XtraBackup.

Adding nodes to a Group Replication cluster can be easy (documented here), but it only works if the existing nodes have retained all the binary logs since the creation of the cluster. Obviously, this is possible if you create a new cluster from scratch. The nodes rotate old logs after some time, however. Technically, if the

gtid_purged

 set is non-empty, it means you will need another method to add a new node to a cluster. You also …

Schema change is one of the crucial tasks in MySQL with huge tables. Schema change can cause locks.

What is gh-ost?

                         gh-ost is a triggerless online schema change for MySQL by Github Engineering .It produces light workload on the master during the schema changes . We need online schema change to alter a table without downtime (locking) in production.pt-online schema change is the most widely used tool for making changes in the tables.gh-ost is just an alternative to pt-online schema change.

Why we have to use gh-ost?

…

MySQL 8.0.13 improves replication lag monitoring by extending the instrumentation for transaction transient errors. These temporary errors, which include lock timeouts caused by client transactions executing concurrently as the slave is replicating, do not stop the applier thread: instead, they cause a transaction to retry.…

A well-known performance booster in MySQL is to set sync_binlog to 0.  However, this configuration alone comes with serious consequences on consistency and on durability (the C and D of ACID); I explore those in this series.  In this post, I give some background on the sync_binlog parameter and I explain part of the problem with setting it to 0 (or to a value different from 1).  The other

This will be a short rant: why is relay_log_space_limit still not dynamic ?

This is obviously a rhetorical question.  I see no reason why this MySQL System Variable is not (yet) dynamic.  Obviously, changing the value of this variable could need replication to be stopped (like for slave_parallel_type, slave_parallel_workers and slave_preserve_commit_order), but at least it would not need a MySQL

Parallel replication has been around for a few years now but is still not that commonly used. I had a customer where the master had a very large write workload. The slave could not keep up so I recommended to use parallel slave threads. But how can I measure if it really helps and is working?

At my customer the

slave_parallel_workers

  was 0. But how big should I increase it, maybe to 1? Maybe to 10? There is a blog post about how can we see how many threads are actually used, which is a great help.

We changed the following variables on the slave:

slave_parallel_type = LOGICAL_CLOCK;
slave_parallel_workers = 40;
slave_preserve_commit_order = ON;

40 threads sounds a lot, right? Of course, this is workload specific: if the transactions are independent it might be …