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Fun with Bugs #94 - On MySQL Bug Reports I am Subscribed to, Part XXVIII

I may get a chance to speak about proper bugs processing for open source projects later this year, so I have to keep reviewing recent MySQL bugs to be ready for that. In my previous post in this series I listed some interesting MySQL bug reports created in December, 2019. Time to move on to January, 2020! Belated Happy New Year of cool MySQL Bugs!

As usual I mostly care about InnoDB, replication and optimizer bugs and explicitly mention bug reporter by name and give link to his other active reports (if any). I also pick up examples of proper (or improper) reporter and Oracle engineers attitudes. Here is the list:

  • Bug #98103 - "unexpected behavior while logging an aborted query in the slow query log".  …
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3 Step Migration of MySQL data to Clickhouse for faster analytics.

Recently one of our client approach Mydbops with Query slowness on a MySQL environment . They deployed the new code for generate the huge reports for the year end analytics data . After the deployment the queries were extremely slow and they struggled lot , then they approached us for the solution. After the analysis, their OLAP database as expected it was IO bound with 100% disk IOPS utilised during the report generation. So, the queries were starving for the Disk IO slows the process .

Problem statement :

  • Reports are majorly focused on two larger log tables ( emp_Report_model , emp_details ) .
  • The report generator (procedure) is using the count(*) statement to stimulate the aggregated data on each call. It is required for their business purpose .
  • Count(*) is terribly slow in MySQL ( Using MySQL 5.7 ) as it …
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Galera Replication flow Architecture

Galera is the best solution for High Availability, It is being used by many peoples world wide . Galera is doing synchronous replication ( really it is Certification based replication ) to keep update the data on group nodes . In this blog I have explained about “How the Galera replication works?” . For the better understanding, I have made an architecture diagram to describe the replication flow . I have also provided the explanation for the key words which has used in the architecture diagram .

Architecture flow Diagram :

What is writeset ?

Writeset contains all changes made to the database by the transaction and append_key of the changed rows .

What is append_key ?

Append_key registers the key of the changed data by the transaction. The key for rows can be represented in three parts as DATABASE NAME, TABLE NAME, PRIMARY KEY . …

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Requirements on NDB Cluster 8.0

In this blog I am going to go through the most important requirements that
NDB Cluster 8.0 is based on. I am going to also list a number of consequences
these requirements have on the product and what it supports.

One slideshare.net I uploaded a presentation of the NDB Cluster 8.0
requirements. In this blog and several accompanying I am going to present the
reasoning that these requirements led to in terms of software architecture, data
structures and so forth.

The requirements on NDB Cluster 8.0 is the following:

1) Unavailability of less than 30 seconds per year (Class 6 Availability)
2) Predictable latency
3) Transparent Distribution and Replication
4) Write and Read Scalability
5) Highest availability even with 2 replicas
6) …

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Original NDB Cluster Requirements

NDB Cluster was originally developed for Network DataBases in the telecom
network. I worked in a EU project between 1991 and 1995 that focused on
developing a pre-standardisation effort on UMTS that later became standardised
under the term 3G. I worked in a part of the project where we focused on
simulating the network traffic in such a 3G network. I was focusing my attention
especially on the requirements that this created on a network database
in the telecom network.

In the same time period I also dived deeply into research literatures about DBMS
implementation.

The following requirements from the 3G studies emerged as the most important:

1) Class 5 Availability (less than 5 minutes of unavailability per year)
2) High Write Scalability as well as High Read Scalability
3) Predictable latency down to milliseconds
4) Efficient API …

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Influences leading to NDB Cluster using a Shared Nothing Model

The requirements on Class 5 availability and immediate failover had two important
consequences for NDB Cluster. The first is that we wanted a fail-fast architecture.
Thus as soon as we have any kind of inconsistency in our internal data structures we
immediately fail and rely on the failover and recovery mechanisms to make the failure
almost unnoticable. The second is that we opted for a shared nothing model where all
replicas are able to take over immediately.

The shared disk model requires replay of the REDO log before failover is completed
and this can be made fast, but not immediate. In addition as one quickly understands
with the shared disk model is that it relies on an underlying shared nothing storage
service. The shared disk implementation can never be more available than the
underlying shared nothing storage service.

Thus it is actually possible to …

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Influences leading to Asynchronous Programming Model in NDB Cluster

A number of developments was especially important in influencing the development
of NDB Cluster. I was working at Ericsson, so when I didn't work on DBMS research
I was deeply involved in prototyping the next generation telecom switches. I was the
lead architect in a project that we called AXE VM. AXE was the cash cow of Ericsson
in those days. It used an in-house developed CPU called APZ. I was involved in some
considerations into how to develop a new generation of the next generation APZ in the
early 1990s. However I felt that the decided architecture didn't make use of modern
ideas on CPU development. This opened for the possibility to use a commercial CPU
to build a virtual machine for APZ. The next APZ project opted for a development
based on the ideas from AXE VM at the end of the 1990s. I did however at this time
focus my full attention to development of NDB Cluster.

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What to Check if MySQL Memory Utilisation is High

One of the key factors of a performant MySQL database server is having good memory allocation and utilization, especially when running it in a production environment. But how can you determine if the MySQL utilization is optimized? Is it reasonable to have high memory utilization or does it require fine tuning? What if I come up against a memory leak?

Let's cover these topics and show the things you can check in MySQL to determine traces of high memory utilization.

Memory Allocation in MySQL

Before we delve into the specific subject title, I'll just give a short information about how MySQL uses memory. Memory plays a significant resource for speed and …

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Make It Smarter: Tuning MySQL Client Request Routing for Tungsten Connector

Overview The Skinny

In this blog post we explore various options for tuning MySQL traffic routing in the Tungsten Connector for better control of the distribution.

A Tungsten Cluster relies upon the Tungsten Connector to route client requests to the master node or optionally to the slaves. The Connector makes decisions about where to route requests based on a number of factors.

This blog post will focus on the Load Balancer algorithms available via configuration that allow you to adjust the routing behavior of the Connector, along with ways to debug the Connector Load Balancer’s routing decisions.

The Question Recently, a customer asked us:

How do I know which load balancer algorithm is in use by the Connector? And how do we enable debug logging for the Connector load balancer?

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MySQL Encryption: How Master Key Rotation Works

In the last blog post of this series, we discussed in detail how Master Key encryption works. In this post, based on what we already know about Master Key encryption, we look into how Master Key rotation works.

The idea behind Master Key rotation is that we want to generate a new Master Key and use this new Master Key to re-encrypt the tablespace key (stored in tablespace’s header).

Let’s remind ourselves what a Master Key encryption header looks like (it is located in tablespace’s header):

From the previous blog post, we know that when a server starts it goes through all encrypted tablespaces’ encryption headers. During that, it remembers the highest KEY ID it read from all the encrypted tablespaces. For instance, if we have three tables with KEY_ID = 3 and one table with KEY ID = 4, it means that …

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