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Displaying posts with tag: Percona XtraDB Cluster (reset)
PXC – Incremental State transfers in detail

IST Basics

State transfers in Galera remain a mystery to most people.  Incremental State transfers (as opposed to full State Snapshot transfers) are used under the following conditions:

  • The Joiner node reports Galera a valid Galera GTID to the cluster
  • The Donor node selected contains all the transactions the Joiner needs to catch up to the rest of the cluster in its Gcache
  • The Donor node can establish a TCP connection to the Joiner on port 4568 (by default)

IST states

Galera has many internal node states related to Joiner nodes.  They currently are:

  1. Joining
  2. Joining: preparing for State Transfer
  3. Joining: requested State Transfer
  4. Joining: receiving State Transfer
  5. Joining: State …
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Bypassing SST in Percona XtraDB Cluster with binary logs

In my previous post, I used incremental backups in Percona XtraBackup as a method for rebuilding a Percona XtraDB Cluster (PXC) node without triggering an actual SST. Practically this reproduces the SST steps, but it can be handy if you already had backups available to use.

In this post, I want to present another methodology for this that also uses a full backup, but instead of incrementals uses any binary logs that the cluster may be producing.

Binary logs on PXC

Binary logs are not strictly needed in PXC for replication, but …

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Bypassing SST in Percona XtraDB Cluster with incremental backups

Beware the SST

In Percona XtraDB Cluster (PXC) I often run across users who are fearful of SSTs on their clusters. I’ve always maintained that if you can’t cope with a SST, PXC may not be right for you, but that doesn’t change the fact that SSTs with multiple Terabytes of data can be quite costly.

SST, by current definition, is a full backup of a Donor to Joiner.  The most popular method is Percona XtraBackup, so we’re talking about a donor node that must:

  1. Run a full XtraBackup that reads its entire datadir
  2. Keep up with Galera replication to it as much as possible (though laggy donors don’t send flow control)
  3. Possibly still be serving application traffic if you don’t remove Donors from rotation.
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TOI wsrep_RSU_method in PXC 5.6.24 and up

I noticed that in the latest release of Percona XtraDB Cluster (PXC), the behavior of wsrep_RSU_method changed somewhat.  Prior to this release, the variable was GLOBAL only, meaning to use it you would:

mysql> set GLOBAL wsrep_RSU_method='RSU';
mysql> ALTER TABLE ...
mysql> set GLOBAL wsrep_RSU_method='TOI';

This had the (possibly negative) side-effect that ALL DDL’s issued on this node would be affected by the setting while in RSU mode.

So, in this latest release, this variable was made to also have a SESSION value, while retaining GLOBAL as well. This has a couple of side-effects that are common to MySQL variables that are both GLOBAL and SESSION:

  • The SESSION copy is made from whatever the GLOBAL’s value is when a new connection (session) is …
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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
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Percona XtraDB Cluster (PXC): How many nodes do you need?

A question I often hear when customers want to set up a production PXC cluster is: “How many nodes should we use?”

Three nodes is the most common deployment, but when are more nodes needed? They also ask: “Do we always need to use an even number of nodes?”

This is what we’ll clarify in this post.

This is all about quorum

I explained in a previous post that a quorum vote is held each time one node becomes unreachable. With this vote, the remaining nodes will estimate whether it is safe to keep on serving queries. If quorum is not reached, all remaining nodes will set themselves in a state where they cannot process any query (even reads).

To get the right size for you cluster, the only question you should answer is: how many nodes can simultaneously fail while leaving the …

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Q&A: High availability when using MySQL in the cloud

Last week I hosted a webinar on using MySQL in the cloud for High Availability (HA) alongside 451 Research analyst Jason Stamper. You can watch the recording and also download the slides (free) here. Just click the “Register” button at the end of that page.

We had several excellent questions and we didn’t have time to get to several of them in the allotted time. I’m posting them here along with the answers. Feel free to ask follow-up questions in the comments below.

Q: Can the TokuDB engine be used in a PXC environment?

A: No, TokuDB cannot currently be used in a PXC environment, the only supported engine in …

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Percona XtraDB Cluster: Quorum and Availability of the cluster

Percona XtraDB Cluster (PXC) has become a popular option to provide high availability for MySQL servers. However many people are still having a hard time understanding what will happen to the cluster when one or several nodes leave the cluster (gracefully or ungracefully). This is what we will clarify in this post.

Nodes leaving gracefully

Let’s assume we have a 3-node cluster and all nodes have an equal weight, which is the default.

What happens if Node1 is gracefully stopped (service mysql stop)? When shutting down, Node1 will instruct the other nodes that it is leaving the cluster. We now have a 2-node cluster and the remaining members have 2/2 = 100% of the votes. The cluster keeps running normally.

What happens now if Node2 is gracefully stopped? Same thing, Node3 knows that Node2 is no longer part of the …

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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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Percona XtraDB Cluster 5.6.24-25.11 is now available

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 …

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