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: …

This blog is about one of the issues encountered by our Remote DBA Team in one of the production servers. We have a setup of MySQL 5.7 Single Primary (Writer) GR with cluster size of  3 . Due to OOM, the MySQL process in the primary node got killed, this repeated over the course of the time.

We all know about the OOM (out of memory), theoretically, it is a process that the Linux kernel employs when the system is critically low on memory.

In a dedicated DB server, when the OOM triggers the direct impact will be on mysqld process since it will be the most memory consuming one.

Going forward will look into the detailed analysis made to tackle the issue of OOM.

DB Environment:-

• Service – Group Replication Cluster
• Cluster Nodes – 3
• GR mode – Single Primary …

Hope everyone aware about known about LVM(Logical Volume Manager) an extremely useful tool for handling the storage at various levels. LVM basically functions by layering abstractions on top of physical storage devices as mentioned below in the illustration.

Below is a simple diagrammatic expression of LVM

         sda1  sdb1   (PV:s on partitions or whole disks)
           \    /
            \  /
          Vgmysql      (VG)
           / | \
         /   |   \
      data  log  tmp  (LV:s)
       |     |    |
      xfs  ext4  xfs  (filesystems)

IOPS is an extremely important resource, when it comes to storage it defines the performance of disk. Let’s not forget PIOPS(Provisioned IOPS) one of the major selling points for AWS and other cloud vendors for production machines such …

Recently we had been bitten by a Systemd limitation at the “Tasks” created per-unit ie., process. This includes both the kernel threads and user-space threads, with each thread counting individually.

Am writing this blog as a reference for someone who might come across this limitation.

We have been actively working on migration DB instances, from one DC to the newly built DC .The instances on the newer DC were provisioned with the latest hardware and latest Debian OS. Below is the detailed spec of the system.

RAM             : 244G
Core             : 44Core
HardDisk.   : SSD
IOPS             : 120K
OS         …

Monitoring MySQL server has never been an easy task. Monitoring also needs to go through many Complex and difficult queries to get the details.

All these problems can be overcome by an excellent command line monitoring tool  called “Innotop”. Innotop comes with many features and different types of modes/options, which helps to monitor different aspects of MySQL  (InnoDB) performance and also helps database administrator to find out what’s wrong going with MySQL server. Innotop helps in monitoring user statistics, mysql replication status,query list, InnoDB I/O informations etc. Another important thing about innotop is it refreshes the data continuously , so we can view realtime statistics.

Innotop is one of the designed based on top utility for linux.

Recently we had encountered a strange issue with replication and temp directory(tmpdir) change while working for one major client.

All the servers under this were running with Percona flavor of MySQL versioned 5.6.38 hosted on a Debian 8(Jessie)

The MySQL architecture setup  is as follows one master with 5 direct slaves under it

Through this blog, we will take you through the issue we had faced and how we fixed ultimately.

Client Request:

There was a simple request from our client to add a column and index to a 16GB production table since the table had foreign keys, to avoid complications we decided to go with online DDL instead of pt-online-schema.

When we started to alter, it got failed due to insufficient space in “tmpdir”.MySQL by default would be using “/tmp” for temp table creating, sorting and other temp operation, Since we had only 5.7G left on the “/” …

Introduction –

Recently i worked on a production issue for one of our client under support .They have a architecture of a three node Galera cluster with one asynchronous slave .

• Node1 – 172.10.2.11
• Node2 – 172.10.2.12
• Node3 – 172.10.2.13
• Replica – 172.10.2.14

Architecture –

The slave(replica) was configured with node3 as replica master. Unfortunately the node 3 was crashed with an OOM killer ,also server has a low gcache size, so when i am trying to start the node 3 , it went to SST . Here the data size was around 2.6 TB , in general for completion of whole SST and joining the node back to cluster will take around  approximately 12 hours.

As i told earlier, the replication slave was under …