MySQL: chained replication M1>S1>S2

In most case simple master-slave replication provides enough level of high-avalability (about 99.9%), read ops balancing and allows non-blocking backups (if you use MyISAM tables since InnoDB tables can be backed up without blocking). But sometimes you may want to setup chained replication with two slaves: first slave replicates from the master, and the second…
Read more

Dumping MySQL database from slave for replication set up

Usually to set up MySQL replication it’s convenient to dump database from current master with –master-data parameter. With this option mysqldump includes commented SQL operator which needs to be issued on slave to set up replication: CHANGE MASTER TO MASTER_LOG_FILE=’mysqld-bin.000008′, MASTER_LOG_POS=687808977; But sometime it’s not very good idea to dump database from master server. For…
Read more

Nginx: embedding Lua into webserver

Lua is a tiny but powerful programming language. Due to its small memory footprint (about hundreds of kilobytes) it’s widely used in application which need to be extended with more complex logic. For instance, Salvatore Sanfilippo has published a  post describing how you can use power of Lua with Redis. It also applied to nginx,…
Read more

Using RRD with Python: short introduction

RRDtool is a great facility which aims to replace MRTG and was written by Tobias Oetiker. RRDtool provides powerful features for collecting and visualizing various system metrics like network traffic, MySQL counters or whatever you want. It’s always good idea to know what is going on under the hood of your server. Managing servers we…
Read more

Fixing ‘Missing dependency Cache::Cache at /usr/share/munin/plugins/mysql_’ error

While installing MySQL plugins for munin in Fedora 15 you may encounter this problem: [root@monitor plugins]# /usr/share/munin/plugins/mysql_ suggest Missing dependency Cache::Cache at /usr/share/munin/plugins/mysql_ line 716. [root@monitor plugins]# It means that your system lacks perl-Cache-Cache and perl-IPC-ShareLite packages. After installation you can proceed: yum install perl-Cache-Cache perl-IPC-ShareLite [root@monitor plugins]# /usr/share/munin/plugins/mysql_ suggest bin_relay_log commands connections files_tables innodb_bpool…
Read more

Cleaning ‘Failed actions’ message in Pacemaker/Corosync cluster setup

Sometimes when using Pacemaker/Corosync-based cluster you can see warning message in crm_mon output: Failed actions: drbd_mysql:0_promote_0 (node=node2.cluster.org, call=11, rc=-2, status=Timed Out): unknown exec error  To clean it up you can use command crm_resource which checks health of resources: [root@node1 ~]# crm_resource -P Waiting for 1 replies from the CRMd. OK [root@node1 ~]# To check…
Read more