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Displaying posts with tag: innodb (reset)
MySQL Performance : TPCC "Mystery" [SOLVED]

The TPCC workload "mystery" exposed in the following post was already clarified the last year, and I've presented explanations about the observed problem during PerconaLIVE-2019. But slides are slides, while article is article ;-)) So, I decided to take a time to write a few lines more about, to keep this post as a reference for further TPCC investigations..

The "mystery" is related to observed scalability issues on MySQL 8.0 under the given TPCC workload -- just that on the old aged DBT-2 workload (TPCC variation) I was getting much higher TPS when running on 2 CPU Sockets, comparing to1 CPU Socket, which is was not at all the case for Sysbench-TPCC.

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An Overview to InnoDB Undo Log

As the name indicates, an undo log record contains information about how to undo the recent changes by a transaction. When a transaction writes data, it always makes writes on the tablespace files. InnoDB Undo log stores copy of data that is being modified by any current transaction. So, at this point in time if any other transaction queries for the original data (row) which is being modified,  the undo logs provide the same and serve the purpose. This is what provides a consistent read view ( based on isolation ) during any data modifications.

Here in the above representation, Transaction T1 modifies the data (Data-1). During the time of modification to ensure the reads are consistent, transactions T2  and T3 are given access only to the copy (previous row version) of Data -1 which is stored in the “UNDO” …

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MySQL InnoDB Cluster Disaster Recovery contingency via a Group Replication Replica

Just recently, I have been asked to look into what a Disaster Recovery site for InnoDB Cluster would look like.

If you’re reading this, then I assume you’re familiar with what MySQL InnoDB Cluster is, and how it is configured, components, etc.

Reminder: InnoDB Cluster (Group Replication, Shell & Router) in version 8.0 has had serious improvements from 5.7. Please try it out.

So, given that, and given that we want to consider how best to fulfill the need, i.e. create a DR site for our InnoDB Cluster, let’s get started.

Basically I’ll be looking at the following scenario:

InnoDB Cluster Source site with a Group Replication Disaster Recovery Site.

Now, just before we get into the nitty-gritty, here’s the scope.

Life is already hard enough, so we want as much automated as possible, so, yes, InnoDB Cluster gets some of that done, but there are other parts we will still have …

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Modern approaches to replacing accumulation user-defined variable hacks, via MySQL 8.0 Window functions and CTEs

A common MySQL strategy to perform updates with accumulating functions is to employ user-defined variables, using the UPDATE [...] SET mycol = (@myvar := EXPRESSION(@myvar, mycol)) pattern.

This pattern though doesn’t play well with the optimizer (leading to non-deterministic behavior), so it has been deprecated. This left a sort of void, since the (relatively) sophisticated logic is now harder to reproduce, at least with the same simplicity.

In this article, I’ll have a look at two ways to apply such logic: using, canonically, window functions, and, a bit more creatively, using recursive CTEs.

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Tuning MySQL/InnoDB Flushing for a Write-Intensive Workload

In this post, the third in a series explaining the internals of InnoDB flushing, we’ll focus on tuning. (Others in the series can be seen at InnoDB Flushing in Action for Percona Server for MySQL and Give Love to Your SSDs – Reduce innodb_io_capacity_max!)

Understanding the tuning process is very important since we don’t want to make things worse or burn our SSDs. We proceed with one section per variable or closely-related variables. The variables are also grouped in sections based on the version of MySQL or Percona Server for MySQL where they are valid. A given variable may be present more …

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MySQL Performance : XFS -vs- EXT4 Story

This post was remaining in stand-by for a long time, specially that I was expecting that observed issues will be fixed soon. But time is going, and the problems are remaining. And I'm constantly asked "why, Dimitri, you're suggesting now to use XFS, while in the past you always suggested EXT4 ??" -- hope the following article will clarify you the "why" and maybe motivate you to do your own evaluations to see how well the things are working for you on your own systems under your own workloads..

NOTE : this will also clarify why the new Double Write did not appear in MySQL 8.0 in 2018, as it was planned, but only recently (

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MySQL Compressed Binary Logs


On a busy server, the binary logs can end up being one of the largest contributors to amount of disk space used. That means higher I/O, larger backups (you are backing up your binary logs, right?), potentially more network traffic when replicas fetch the logs, and so on. In general, binary logs compress well, so it has been a long time wish for a feature that allowed you to compress the logs while MySQL are still using them. Starting from MySQL 8.0.20 that is now possible. I will take a look at the new feature in this post.


The binary log compression feature is controlled by two variables, one for enabling the feature and …

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Setting up an InnoDB Cluster With a Few Lines of Code

In this day and age, large enterprise companies make use of Ansible, Puppet, or Chef to provision MySQL servers, be it replica sets or clusters. This eases the burden of deployment and workflow management.

However, for some smaller companies, the learning curve hampers the immediate adoption of automation software. This is where the MySQL Shell helps, by allowing you to deploy an N-node InnoDB Cluster or ReplicaSet in less than 60 lines of code.

The Requirements

  • Percona Server for MySQL version 8.0.17 or later, preferable version 8.0.19, each node started as standalone servers
  • Percona MySQL Shell 8.0 or equivalent upstream version
  • MySQL root user and password or equivalent user with grant option
  • Hostname configured on each node, can be done with …
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What is New in MySQL NDB Cluster 8.0.20

MySQL NDB Cluster 8.0.20 new features 

This post is about changes in the implementation of NDB Cluster from MySQL NDB Cluster 8.0 through 8.0.20, as compared to earlier release series. We have included only those of MySQL NDB Cluster 8.0.20 new features which are really interesting and can directly influence / make an impact to performance, scalability and reliability:

  • MySQL NDB Cluster  development is in parallel with the development of  MySQL Server going forward. What does that mean for MySQL customers globally NDB 8.0 is developed in, built from, and released with the MySQL 8.0 source code tree and numbering scheme for NDB Cluster 8.0 releases follows the scheme for MySQL 8.0 ( starting with version 8.0.13).
  • As of NDB 8.0.18, The identifiers can use up to 64 bytes for databases and tables (the 63-byte limit on identifiers is removed ).
  • Generated names for foreign keys …
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MySQL Performance : The New InnoDB Double Write Buffer in Action

The new MySQL-8.0.20 release is coming with re-designed InnoDB Double Write Buffer (DBLWR), and, indeed, it's one huge historical PITA less.. -- why it was so painful and cost us much blood in the past, I could not better explain than already done it in the following article yet from 2018 about MySQL on IO-bound workloads.. The story is not complete, as it's missing the 2019's chapter (will tell it later, np) -- but if you'll (re)read the mentioned above article first, you'll better understand the next ;-))

But at least the current post is only about good news now -- the new DBLWR and how it helps to solve historical MySQL performance problems ! -- and as one picture is better than million words, I'll try to save 3M words here (as there are 3 pictures in this article ;-))

Well, I'll also skip all new design details …

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