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Displaying posts with tag: XtraDB Cluster (reset)
Galera Cache (gcache) is finally recoverable on restart

This post describes how to recover Galera Cache (or gcache) on restart.

Recently Codership introduced (with Galera 3.19) a very important and long awaited feature. Now users can recover Galera cache on restart.

Need

If you gracefully shutdown cluster nodes one after another, with some lag time between nodes, then the last node to shutdown holds the latest data. Next time you restart the cluster, the last node shutdown will be the first one to boot. Any followup nodes that join the cluster after the first node will demand an SST.

Why SST, when these nodes already have data and only few write-sets are missing? The DONOR node caches missing write-sets in Galera cache, but on restart this cache is wiped clean and restarted fresh. So the DONOR node …

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All You Need to Know About GCache (Galera-Cache)

This blog discusses some important aspects of GCache.

Why do we need GCache?

Percona XtraDB Cluster is a multi-master topology, where a transaction executed on one node is replicated on another node(s) of the cluster. This transaction is then copied over from the group channel to Galera-Cache followed by apply action.

The cache can be discarded immediately once the transaction is applied, but retaining it can help promote a node as a DONOR node serving write-sets for a newly booted node.

So in short, GCache acts as a temporary storage for replicated transactions.

How is GCache managed?

Naturally, the first choice to cache these write-sets is to use memory allocated pool, which is governed by gcache.mem_store. However, this is deprecated and buggy and shouldn’t be used.

Next …

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Percona XtraDB Cluster 5.7.14-26.17 GA is now available

This Percona XtraDB Cluster 5.7.14-26.17 GA release is dedicated to the memory of Federico Goncalvez, our colleague with Percona’s Uruguayan team until his tragic death on September 6, 2016.

Fede, we miss you.

Percona announces the first general availability (GA) release in the Percona XtraDB Cluster 5.7 series on September 29, 2016. Binaries are available from the downloads area or our software repositories.

The full release notes are available …

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Percona XtraDB Cluster 5.7.12 RC1 is now available

Percona announces the first release candidate (RC1) in the Percona XtraDB Cluster 5.7 series on August 9, 2016. Binaries are available from the downloads area or our software repositories.

Percona XtraDB Cluster 5.7.12-5rc1-26.16 is based on the following:

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Percona XtraDB Cluster on Ceph

This post discusses how XtraDB Cluster and Ceph are a good match, and how their combination allows for faster SST and a smaller disk footprint.

My last post was an introduction to Red Hat’s Ceph. As interesting and useful as it was, it wasn’t a practical example. Like most of the readers, I learn about and see the possibilities of technologies by burning my fingers on them. This post dives into a real and novel Ceph use case: handling of the Percona XtraDB Cluster SST operation using Ceph snapshots.

If you are familiar with Percona XtraDB Cluster, you know that a full state snapshot transfer (SST) is required to provision a new cluster node. Similarly, SST can also be triggered when a cluster node happens to have a corrupted …

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Galera Error Failed to Report Last Committed (Interrupted System Call)

In this blog, we’ll discuss the ramifications of the Galera Error Failed to Report Last Committed (Interrupted System Call).

I have recently seen this error with Percona XtraDB Cluster (or Galera):

[Warning] WSREP: Failed to report last committed 549684236, -4 (Interrupted system call)

It was posted in launchpad as a bug in 2013: https://bugs.launchpad.net/percona-xtradb-cluster/+bug/1434646

My colleague Przemek replied, and explained it as:

Reporting the last committed transaction is just a part of the certification index purge process. In case it fails for some reason (it occasionally does), the cert index purge may be a little delayed. But it does not mean the transaction was not applied successfully. This is a warning after all.

If we look up this error in the source code, we realize …

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Better high availability: MySQL and Percona XtraDB Cluster with good application design

High Availability

Have you ever wondered if your application should be able to work in read-only mode? How important is that question?

MySQL seems to be the most popular database solution for web-based products. Most typical Internet application workloads consist of many reads, with usually few writes. There are exceptions of course – MMO games for instance – but often the number of reads is much bigger then writes. So when your database infrastructure looses its ability to accept writes, either because traditional MySQL replication topology lost its master or Galera cluster lost its quorum, why would you want to the application to declare total …

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Playing with Percona XtraDB Cluster in Docker

Like any good, thus lazy, engineer I don’t like to start things manually. Creating directories, configuration files, specify paths, ports via command line is too boring. I wrote already how I survive in case when I need to start MySQL server (here). There is also the MySQL Sandbox which can be used for the same purpose.

But what to do if you want to start Percona XtraDB Cluster this way? Fortunately we, at Percona, have engineers who created automation solution for starting PXC. This solution uses Docker. To explore it you need:

  1. Clone the pxc-docker repository:
    git clone https://github.com/percona/pxc-docker
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MaxScale: A new tool to solve your MySQL scalability problems

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 …

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Galera data on Percona Cloud Tools (and other MySQL monitoring tools)

I was talking with a Percona Support customer earlier this week who was looking for Galera data on Percona Cloud Tools. (Percona Cloud Tools, now in free beta, is a hosted service providing access to query performance insights for all MySQL uses.)

The customer mentioned they were already keeping track of some Galera stats on Cacti, and given they were inclined to use Percona Cloud Tools more and more, they wanted to know if it was already supporting Percona XtraDB Cluster. My answer was: “No, not yet: you can install agents in each node (the regular way in the first node, then …

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