Discover how to troubleshoot a MySQL replica IO thread stuck in a connecting state. Learn about the replication architecture, security group rules for AWS EC2 instances, and how to address common issues like network restrictions and bind address configuration.

MySQL is a powerful database management and a widely used cloud database service. One of its key features is the ability to create replicas of a master database to improve its availability and scalability. However, at times the IO thread in a MySQL replica may get stuck in a connecting state, which can cause replication issues and affect the overall data consistency …

ProxySQL is an open-source MySQL proxy server, meaning it serves as an intermediary between a MySQL server and the applications that access its databases. ProxySQL can improve performance by distributing traffic among a pool of multiple database servers.

Consider 2 slaves are routed under Proxysql , In any one of the slave, if the replication is broken, we could still see the traffic routing to the broken replication slave. We can make Proxy to not send traffic to broken replication slave, by setting appropriate value to the variable mysql-monitor_slave_lag_when_null

…

MySQL 8.0.30 was released on 26-07-2022. It has a good list of features.

• Generated Invisible Primary Key
• Dynamic Redo log Sizing
• Instruments to monitor group replication memory
• Support for Ubuntu 22.04

A most notable feature for Database Administrators and database reliability engineers is Dynamic redo logging.

The more widely adopted open-source backup tool is Xtrabackup. The change in the redo log design has affected this hot backup tool.

2022-10-04T18:40:08.211998+05:30 0 [Note] [MY-011825] [Xtrabackup] recognized server arguments: --datadir=/var/lib/mysql 
2022-10-04T18:40:08.212264+05:30 0 [Note] [MY-011825] [Xtrabackup] recognized client arguments: …

This is one of the exciting troubleshooting related to XA transactions let’s dive in. Let me provide a few backgrounds.

For one of our clients, when we try to drop a table, it is waiting for metadata lock. On debugging it is one of the XA transactions is holding the shared write lock and causing metadata lock on all the other local transactions.

Let us view the metadata locks from the Performance Schema.

We have planned for archiving the data to improve the DB performance and to reclaim the space. We were evaluating Compression in InnoDB and TokuDB. To find out the best compression method. We started benchmarking the compression ratio between InnoDB and TokuDB.

Everything goes well for some time, but after a few hours got an error message that can’t able to insert the data into the TokuDB table due to storage being full. It is so strange and the host has enough free space.

Table structure:-

mysql> show create table mydbops.tokudb\G
*************************** 1. row ***************************
       Table: tokudb
Create Table: CREATE TABLE `tokudb` (
  `ID` int DEFAULT NULL,
  `Name` longtext,
  `Image` blob
) ENGINE=TokuDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (2.18 sec)

mysql> show create table mydbops.innodb\G
*************************** 1. row …

To copy the data of the particular column of the table to another table/server, We have an option to export the data as CSV and import the data back to a different table. But when the table size is large and we need to copy the data only for the required data to the target table will cause the load in the server since the table scanning is huge.

To overcome this, we have the pt-archiver copy the data from the source table to the destination as a whole or only for required columns. And also we can do this in a controlled manner as well. So there will be no performance impact even on the production time.

Source table structure :

mysql> show create table source\G
*************************** 1. row ***************************
       Table: source
Create Table: CREATE TABLE `source` (
  `id` int unsigned NOT NULL …

We all tried various alternative methods for modifying the table structure, but pt-online-schema-change (pt-osc) is the most convenient and preferred method for performing the alter online. It has more granular control too. But it may lead to data loss if proper precautionary steps are not taken care of.

In this blog, we are going to modify a column to a unique key using pt-osc, below I have shared the table structure.

mysql> show create table test\G
* 1. row *
Table: test
Create Table: CREATE TABLE test (
Personid int(11) NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255) DEFAULT NULL,
Age int(11) DEFAULT NULL,
PRIMARY KEY (Personid)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

I have inserted the data of 1000 rows using …

Over the decades we have been reading the MySQL error log from the server system file, if there are any issues in MySQL or any unknown restart happened , generally we look at the mysql error log.

By default MySQL error log can be found in the default path /var/log/mysqld.log , or it can be explicitly configured using the variable log_error.

Few drawbacks using MySQL error log as FILE

• Possibility of missing genuine errors while reading lengthy information.
• Filtering of errors for the particular date and timeframes.
• Cannot provide the DB server access to developers because of fear of mishandling DB servers.

To overcome the above issues , from MySQL …

In a perfect world, we expect all software to run flawlessly and never have problems such as bugs and crashes. We also know that this perfect world doesn’t exist and we better be as prepared as possible to troubleshoot those types of situations. Historically, generating core dumps has been a task delegated to the kernel. If you are curious about how to enable it via Linux kernel, you can check out Getting MySQL Core file on Linux. There are a few drawbacks that pose either a limitation or a huge strain to get it working, such as:

• System-wide configuration required. This is not something DBA always has access to.
• Inability or very difficult to enable it for a specific binary only. Standards ways enable it for every software running on the box.
• Nowadays, with cloud and containers, this task has become even …

A few days ago one of our intern @mydbops reached me with a SQL query. The query scans only a row according to the execution plan. But query does not seems optimally performing.

Below is the SQL query and its explain plan. ( MySQL 5.7 )

select username, role from user_roles where username= '9977223389' ORDER BY role_id DESC LIMIT 1;

Execution plan and table structure

*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: user_roles
   partitions: NULL
         type: index
possible_keys: NULL
          key: PRIMARY
      key_len: 4
          ref: NULL
         rows: 1
     filtered: 10.00
        Extra: Using where
1 row in set, 1 warning (0.00 sec)

show create table user_roles\G
*************************** 1. row ***************************
       Table: …