Ever since MySQL replication has existed, people have dreamed of a good solution to automatically split read from write operations, sending the writes to the MySQL master and load balancing the reads over a set of MySQL slaves. While if at first it seems easy to solve, the reality is far more complex.

First, the tool needs to make sure it parses and analyses correctly all the forms of SQL MySQL supports in order to sort writes from reads, something that is not as easy as it seems. Second, it needs to take into account if a session is in a transaction or not.

While in a transaction, the default transaction isolation level in InnoDB, Repeatable-read, and the MVCC framework insure that you’ll get a consistent view for the duration of the transaction. That means all statements executed inside a transaction must run on the master but, when the transaction commits or rollbacks, the following select statements on the session can be again …

Percona is glad to announce the new release of Percona XtraDB Cluster 5.6 on June 3rd 2015. Binaries are available from downloads area or from our software repositories.

Based on Percona Server 5.6.24-72.2 including all the bug fixes in it, Galera Replicator 3.11, and on …

Some applications have a heavy write workload on a few records – for instance when incrementing a global counter: this is called a write hotspot. Because you cannot update the same row simultaneously from multiple threads, this can lead to performance degradation. When using Percona XtraDB Cluster (PXC), some users try to solve this specific issue by writing on multiple nodes at the same time. Good idea or bad idea? Read on!

Simultaneous writes on a standalone InnoDB server

Say you have these 3 transactions being run simultaneously (id is the primary key of the table):

# T1
UPDATE t SET ... WHERE id = 100
# T2
UPDATE t SET ... WHERE id = 100
# T3
UPDATE t SET ... WHERE id = 101

All transactions will require a row lock on the record they want to modify. So T3 can commit at the same time than T1 and/or T2, because it will …

I often talk with people who are very interested in the features of Percona XtraDB Cluster (PXC) such as synchronous and parallel replication, multi-node writing and high availability. However some get confused when operating a real PXC cluster because they do not fully realize the implications of these features. So here is a fun way to test your PXC knowledge: try to solve these 12 questions related to PXC! (you will find the answers at the end of the post.)

Workload

1. With Galera 3.x, support for MyISAM is experimental. When can we expect to have full MyISAM support?
a. This will never happen as Galera is designed for transactional storage engines.
b. This is planned for Galera 4.0.

2. Why aren’t all workloads a good fit for PXC?
a. Execution plans can change compared to a regular MySQL server, so performance is sometimes not as good as with a regular MySQL server.
b. Large …

Percona Toolkit is one of our most mature open source applications. Derived from Maatkit and Aspersa, Percona Toolkit has evolved significantly over the years. The software now contains 32 tools, over 4,000 tests, and has been downloaded over 250,000 times. Anyone who manages a database – from DBAs to system administrators to even software developers – benefits from Percona Toolkit’s ability to perform a variety of MySQL server and system tasks that are too difficult or complex to perform manually.

We continue to make Percona Toolkit better each month. Over the last 9 months alone Percona has had 6 releases and resolved nearly 50 issues.

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My webinar “Multi-threaded Replication in MySQL 5.6 and 5.7″ on February 25 generated several excellent questions following the presentation (available here for playback along with the slides). I didn’t have time to answer many of the questions during the session and so in this post I answer all of them. Thanks to everyone who attended!

Q: What do you expect from MTS with logical clock? Do you think performance would be good as with per database?
A: MTS with 5.6 is not usable if you have a single database. I do not have numbers, but this is quite frequent. With 5.7 everyone should be able to benefit from multi-threaded replication.

Q: When MySQL 5.6 was released, performance of MTS was lower, than in 5.5, for example. Is this addressed now?
A: I am not sure which …

Percona is glad to announce the new release of Percona XtraDB Cluster 5.6 on March 5th 2015. Binaries are available from downloads area or from our software repositories.

Based on Percona Server 5.6.22-72.0 including all the bug fixes in it, Galera Replicator 3.9, and on Codership wsrep API 25.8, Percona XtraDB Cluster 5.6.22-25.8 is now the current …

As the need for information grows so does the size of data we need to keep in our databases. SST is unavoidable for spinning up new nodes in a PXC cluster and when datasets reach the “terra-byte” range this becomes ever more cumbersome requiring many hours for a new node to synchronize.

More often that not, it is necessary to implement custom “wsrep_sst” scripts or resort to manual synchronization processes. Luckily cloud providers provide convenient methods to leverage disk snapshots that can be used to quickly transfer data between nodes.

This article deals with the actions needed to perform a snapshot on Google’s Compute Engine (GCE) infrastructure. A similar method can be used on AWS EC2 instances using EBS snapshots or any other form of snapshots such as LVM, ZFS or SAN. The steps described can be …

This past week was marked by a series of personal findings related to the use of Global Transaction IDs (GTIDs) on Galera-based clusters such as Percona XtraDB Cluster (PXC). The main one being the fact that transactions touching MyISAM tables (and FLUSH PRIVILEGES!) issued on a giving node of the cluster are recorded on a GTID set bearing the node’s server_uuid as “source id” and added to the binary log (if the node has binlog enabled), thus being replicated to any async replicas connected to it. However, they won’t be replicated across the cluster (that is, all of this is by design, if wsrep_replicate_myisam is …

Say you have a cluster with 3 nodes using Percona XtraDB Cluster (PXC) 5.6 and one asynchronous replica connected to node1. If asynchronous replication is using GTIDs, moving the replica so that it is connected to node2 is trivial, right? Actually replication can easily break for reasons that may not be obvious at first sight.

Summary

Let’s assume we have the following setup with 3 PXC nodes and one asynchronous replica:

Regarding MySQL GTIDs, a Galera cluster behaves like a distributed master: transactions coming from any node will use the same auto-generated uuid. This auto-generated uuid is related to the Galera uuid, it’s neither ABC, nor DEF, nor GHI.

Transactions executed for …