In this blog post, we’ll look at how we’ve improved wsrep-stages and related instrumentation in Percona XtraDB Cluster.

Introduction

When you execute a workload and need to find out what the given thread is working on, “SHOW PROCESSLIST” comes to the top of your mind. It is an effective way to track the thread status. We decided to improve the stages in Percona XtraDB Cluster to make “SHOW PROCESSLIST” more meaningful.

In the blog below, we will check out the different wsrep-stages and the significance associated with them.

Loading of data

Running a simple insert/sysbench prepare workload. The state is stable as it mainly captures …

In this blog post, we’ll look at a transaction replay anomaly in Percona XtraDB Cluster.

Introduction

Percona XtraDB Cluster/Galera replays a transaction if the data is non-conflicting but, the transaction happens to have conflicting locks.

Anomaly

Let’s understand this with an example:

• Let’s assume a two-node cluster (node-1 and node-2)
• Base table “t” is created as follows:

create database test;
use test;
create table t (i int, c char(20), primary key pk(i)) engine=innodb;
insert into t values (1, 'abc'), (2, 'abc'), (4, 'abc');
select * from t;
mysql> select * from t;
+---+------+
| i | c |
+---+------+
| 1 | abc |
| 2 | abc |
| 4 | abc |
+---+------+

• node-2 starts runs a transaction (trx-2):
…

In this blog post, we’ll look at how increasing the fc_limit can affect SELECT latency.

Introduction

Recent Percona XtraDB Cluster optimizations have exposed fc_limit contention. It was always there, but was never exposed as the Commit Monitor contention was more significant. As it happens with any optimization, once we solve the bigger contention issues, smaller contention issues start popping up. We have seen this pattern in InnoDB, and Percona XtraDB Cluster is no exception. In fact, it is good because it tells us that we are on the right track.

If you haven’t yet checked the performance blogs, then please visit here and …

In this blog post, we’ll look at a feature that recently added to Percona XtraDB Cluster 5.7.16, that makes it easier to configure Percona XtraDB Cluster SSL for all related communications. It uses mode “encrypt=4”, and configures SSL for both IST/Galera communications and SST communications using the same SSL files. “encrypt=4” is a new encryption mode added in Percona XtraDB Cluster 5.7.16 (we’ll cover it in a later blog post).

If this option is used, this will override all other Galera/SST SSL-related file options. This is to ensure that a consistent configuration is applied. Using this option also means that the Galera/SST communications are …

In this blog post, we’ll look at how Percona XtraDB Cluster uses IST.

Introduction

Percona XtraDB Cluster uses the concept of an Incremental State Transfer (IST). When a node of the cluster leaves the cluster for a short period of time, it can rejoin the cluster by getting the delta set of missing changes from any active node in the cluster.

This process of getting the delta set of changes is named as IST in Percona XtraDB Cluster.

Tracking IST Progress

The number of write-sets/changes that the joining node needs to catch up on when rejoining the cluster is dictated by:

1. The duration the node was not present in the cluster
…

In this blog post, we’ll look at the actions and efforts Percona experts took to scale Percona XtraDB Cluster.

Introduction

When we first started analyzing Percona XtraDB Cluster performance, it was pretty bad. We would see contention even with 16 threads. Performance was even worse with sync binlog=1, although the same pattern was observed even with the binary log disabled. The effect was not only limited to OLTP workloads, as even other workloads (like update-key/non-key) were also affected in a wider sense than OLTP.

That’s when we started analyzing the contention issues and found multiple problems. We will discuss all these problems and the solutions we adapted. But …

Percona announces the release of Percona XtraDB Cluster 5.7.17-27.20 on March 16, 2017. Binaries are available from the downloads section or our software repositories.

NOTE: You can also run Docker containers from the images in the Docker Hub repository.

Percona XtraDB Cluster 5.7.17-27.20 is now the current release, based on the following:

• …

Percona announces the release of Percona XtraDB Cluster 5.6.35-26.20 on March 10, 2017. Binaries are available from the downloads section or our software repositories.

Percona XtraDB Cluster 5.6.35-26.20 is now the current release, based on the following:

• Percona Server 5.6.35-80.0
• Galera Replication library 3.20
• wsrep API version 26

All Percona software is open-source and free. Details of this …

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 …

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 …