11 Apr

Reset root password on Galera Cluster (Percona or MariaDB)

We have known methods to reset MySQL root password but in this post we’ll see how that works for a Galera Cluster; may it be Percona XtraDB Cluster or MariaDB Galera cluster.

Basically a Galera Cluster is bunch of MySQL nodes working together in synchronous replication. The user credential is common to all (Ideally of-course)! Let’s see how straight¬† forward it is to reset password on a Percona Xtradb Cluster lab.

To reset the root password on a standard MySQL instance you may choose either of init-file or skip-grant-tables way. Read More

02 Mar

MySQL to Galera Cluster Migration, Deadlock, Back to basics

This post is a lab experiment learning from migration to the Percona Xtradb Cluster (Galera) and a very unexpected DEADLOCK scenario which took me back to basics.

(root@localhost) [test]>insert into app values (1);
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction

Little background:

We needed to work on migrating the standard MySQL replication to a Galera (Percona Xtradb Cluster).

Previous configuration being one Master with two slaves detailed as follows:
server-1: MySQL community 5.6 serving as Master
server-2: MySQL community 5.6 serving as Slave
server-3: MySQL community 5.6 serving as Slave

We wanted to migrate above MySQL standard replication setup to Percona Xtradb Cluster (PXC 5.6) as following 3 nodes:

mysql to galera migration

Read More

13 Jun

Restoring MySQL Database from xtrabackup – facepalm moments

In this post we’ll see some facepalm moments during MySQL database restore from Percona Xtrabackup.¬† I think: “To mistake is Homo-sapiens, to learn from them is Homo-sapiens-sapiens.”

A typical way to restore MySQL backup from Xtrabackup involves following steps:

– Ship or stream backup to destination.
– Perform extraction of the compressed database backup.
– Perform apply-log step to prepare the backup.
– Bring up MySQL.
– Configure replication (if that’s required).

We have a lot of documentation & blogs explaining that,¬† but let’s see how our MySQL DBA enjoyed the facepalm moments.

Read More

07 Dec

corrupted / crashed MyISAM + mysql_repair_threads = stuck “Repair with N threads”

In this post we’re going to look at how changing MySQL variable mysql_repair_threads for betterment of a repair table command became root cause of an instance reboot. Also how repair with n threads message tracks down to this.

MyISAM is notorious for table crashes and always need a table repair as a quick remedy.

 Table 'myisam_table' is marked as crashed and should be repaired.

After seeing above error we quickly jump on to one of the following

 repair table myisam_table
 myisamchk -r -q myisam_table

Ofcourse there are more options but that’s not something we’re talking here.

Once this become regular and/or table is large, we look forward to speedup the operation. Then stands out one variable that comes as a ray of hope: mysql_repair_threads
As MySQL documentation says “for value greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process.” Read More

04 Dec

Fixing inconsistency on MySQL Slave of Galera Cluster

Checksum is a standard practice among DBAs to verify the data consistency across replicated nodes. In this post we’re going to review the syncing options for an inconsistent MySQL slave of Galera cluster node.

Here we’re assuming a setup of regular replication to a MySQL instance from one of the Galera cluster nodes.
PXC-slave-checksum Read More

-- Kedar Vaijanapurkar --