10 Apr

Still have MySQL 5.6 variable binlog_error_action as IGNORE_ERROR?

Recently, we were affected by an ignored configuration option introduced in MySQL 5.6. This incident caused us to perform extended planning of downtime and the rebuilding of the slave. In this post, we’ll discuss our encounter with binlog_error_action and likely bad default.

The incident started with an alert from our monitoring platform that a check failed to verify a MySQL master’s binary log coordinates. My colleague working from the other side of the globe observed the following:

mysql> show master status;
    Empty set (0.00 sec)
    mysql> show binary logs;
    ERROR 1381 (HY000): You are not using binary logging

Interestingly, the MySQL slave was still reporting that everything was okay!

mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: master
                  Master_User: replicator
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000186
          Read_Master_Log_Pos: 1069066810
               Relay_Log_File: mysqld-relay-bin.000245
                Relay_Log_Pos: 1069067004
        Relay_Master_Log_File: mysql-bin.000186
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
                   Last_Errno: 0
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 1069066810
              Relay_Log_Space: 1069067296
              Until_Condition: None
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
        Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
               Last_SQL_Errno: 0
             Master_Server_Id: 23294781
                  Master_UUID: 7e2e60eb-39fb-11ea-a248-005056b589fd
             Master_Info_File: mysql.slave_master_info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
           Master_Retry_Count: 86400
           Retrieved_Gtid_Set: 7e2e60eb-39fb-11ea-a248-005056b589fd:50961813-81101493
            Executed_Gtid_Set: 2366bbb5-39fb-11ea-a246-005056b5f82f:1-818,
                Auto_Position: 1
1 row in set (0.00 sec)

Guess what my colleague saw in the error log?

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08 Oct

ProxySQL Configuration File & Startup Process Explained

When learning ProxySQL, we have seen some confusion around the configuration and especially around the usage of the configuration file. In this post, we will explain how ProxySQL treats its internal configuration and its configuration file.

The Proxysql.Cnf

For the initial startup, the configuration is loaded from the /etc/proxysql.cnf file. At this time, the configuration file will be parsed and the settings will be stored in the embedded SQLite database. From this point onwards, the settings will be accessed from the SQLite database.

However, there are four configuration settings which are always parsed from the config file, even when the SQLite database is present. This places a requirement for the configuration file to always be in the place, if missing, ProxySQL terminates.

  • datadir: The path of ProxySQL datadir which stores database file, logs.
  • restart_on_missing_heartbeats (new in 1.4.4): If MySQL threads miss restart_on_missing_heartbeats (number of) heartbeats, proxysql will raise a SIGABRT signal and restart. Default is 10.
  • execute_on_exit_failure (new in 1.4.4): If set, ProxySQL’s parent process will execute the defined script every time ProxySQL crashes. It is recommended to use this setting to generate an alert or log the event. 
  • errorlog (new in 2.0.0): The file to be used as error-log. Defaults to ${datadir}/proxysql.log
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09 Apr

mysql database backup shell script with status email

This post is for the backup script for MySQL database on Linux with mail. It’s a linux shell script for taking logical backup using mysqldump and sending status email.

The backup shell script works as follows:
– The script takes backup using mysqldump and compresses it.
– Upon success, it will attempt to ship the backup to specified offsite location.
– Upon detecting failure in any of the above step, it will send out failure email.
– Upon overall success, it will sendout success email with execution time and present backups list.

You might be looking for setting up physical backups for mysql using Holland backup framework.

Following is the code for MySQL backup shell script using mysqldump with status email.

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07 Sep

MySQL 8 Resource Group – introduction and dynamic allocation

MySQL 8 is GA and it has a variety of new features. Recently, we happened to work with resource groups to restrict resource utilization for a MySQL thread.

That’s why I thought of writing this blog post: to give you a quick introduction to resource groups, an idea of how to dynamically allocate them and to discuss a related bug report.

Introduction To Resource Groups:

A resource group, a new feature in MySQL 8, is the entity that defines the allowed resources consumption for threads pertaining to that group. Group attributes enable control over resources and hence the database threads get restricted with those limits.

Resource groups introduce the following associated components:
1. SQL to manage the resource groups (create, alter, assign, drop).
2. Resource groups related privileges.
3. The information_schema.resource_groups table, which holds groups details.
4. A new column was added to the performance_schema.threads table to show us the assignments of threads to respective resource groups.

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13 Aug

Galera cluster to AWS Aurora migration & HA_ERR_FOUND_DUPP_KEY

In this post we will see a case study of a Galera Cluster migration to AWS Aurora and quick solution to the replication issue.

A friend received an error in a Master-Master replication as follows:

Could not execute Write_rows event on table _database._table; Duplicate entry '65eJ8RmzASppBuQD2Iz73AAy8gPKIEmP-2018-08-03 08:30:03' for key 'PRIMARY', Error_code: 1062; handler error HA_ERR_FOUND_DUPP_KEY; the event's master log mysql-bin-changelog.000010, end_log_pos 1107814

We talked about it and I immediately started blabbering cons of writing on both masters, how to handle, roles of apps and so on. He intervened and revealed, it is Galera Cluster replicated to Aurora and he is not writing on Aurora.

He was actually migrating his Galera Cluster to Aurora and master-master was to support his rollback plans. Consider following diagram for simplicity of understanding:

galera to aws migration - sample architecture

galera to aws migration – sample architecture

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-- Kedar Vaijanapurkar --