Databases, Systems & Networks

Source: nixCraft

How do I use mysqldump command with Unix shell pipes?

The mysqldump client is a backup program which is used to dump a database or a collection of databases for backup or transfer to another SQL server (not necessarily a MySQL server). The dump typically contains SQL statements to create the table, populate it, or both. However, mysqldump can also be used to generate files in CSV, other delimited text, or XML format. The syntax is as follows to dump a database called foo to the remote server called server1.cyberciti.biz:

mysqldump db-name | mysql -h server1.dbsysnet.com db-name
mysqldump foo | mysql -h server1.dbsysnet.com foo

However, I recommend using VPN or ssh client to secure data transfer using the shell pipes as follows:

mysqldump db-name | ssh user@server1.dbsysnet.com mysql db-name
mysqldump -u vivek -p'myPassWord' foo | ssh vivek@server1.dbsysnet.com mysql -u backup -p'myPassword' bar

Source: nixCraft

I‘m a new MySQL server user. My server is running on a CentOS Linux. How can I check the number of active MySQL connections on Linux based system?

You can use the following commands on Linux or Unix-like systems:

• mysqladmin status command
• MySQL show status command
• netstat or ss commands

mysqladmin status command example

Open the terminal App or login to the remote server using ssh:

ssh mandrake@dbsysnet.com

Type the following command to get a short status message from the MySQL server:

mysqladmin status
## OR ##
mysqladmin status -u root -p
## OR ##
mysqladmin status -h db1.dbsysnet.com -u root -p

Sample outputs:

Uptime: 691356  Threads: 5  Questions: 83237956  Slow queries: 102736  Opens: 3585  Flush tables: 1  Open tables: 1019  Queries per second avg: 120.398

MySQL show status command to see open database connections example

First, connect to the your mysql server:

mysql -u root -p

Type the following sql query to see the number of connection attempts to the MySQL serverincludes both failed and successful connection attempts:

mysql> show status like 'Conn%';

Sample outputs:

You can use the following sql command to see the number of currently open connections at mysql> prompt:

mysql> show status like '%onn%';
+--------------------------+---------+
| Variable_name            | Value   |
+--------------------------+---------+
| Aborted_connects         | 7       |
| Connections              | 6304067 |
| Max_used_connections     | 85      |
| Ssl_client_connects      | 0       |
| Ssl_connect_renegotiates | 0       |
| Ssl_finished_connects    | 0       |
| Threads_connected        | 7       | <---- No of currently open connections
+--------------------------+---------+
7 rows in set (0.00 sec)

Lire la suite…

Source: nixCraft

I‘m a new Ubuntu Linux user and my cloud hosting company installed MySQL server by default. I need to remove it and delete it from my server as I have no use of MySQL server. How can I uninstall MySQL on a Ubuntu based systems?

Typically following Mysql packages are installed on the Debian or Ubuntu Linux systems:

• mysql-client – The latest version of MySQL database client.
• mysql-server – The latest version of MySQL database server.
• mysql-common – MySQL database common files.

How do I uninstall Mysql server?

Just use the apt-get command as follows remove both MySQL server and client in Ubuntu Linux:

sudo apt-get --purge remove mysql-client mysql-server mysql-common
sudo apt-get autoremove

Sample outputs (pay attention to package names):

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  linux-headers-3.2.0-31-virtual linux-headers-3.2.0-31
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  libdbd-mysql-perl* libmysqlclient18* mysql-client* mysql-client-5.5* mysql-common* mysql-server*
  mysql-server-5.5*
0 upgraded, 0 newly installed, 7 to remove and 0 not upgraded.
After this operation, 67.5 MB disk space will be freed.
Do you want to continue [Y/n]? y
(Reading database ... 105097 files and directories currently installed.)
Removing mysql-server ...
Removing mysql-server-5.5 ...
mysql stop/waiting
Purging configuration files for mysql-server-5.5 ...
Removing mysql-client ...
Removing mysql-client-5.5 ...
Removing libdbd-mysql-perl ...
Removing libmysqlclient18 ...
Purging configuration files for libmysqlclient18 ...
Removing mysql-common ...
Purging configuration files for mysql-common ...
dpkg: warning: while removing mysql-common, directory '/etc/mysql' not empty so not removed.
Processing triggers for ureadahead ...
Processing triggers for man-db ...
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place

Delete /etc/mysql/ directory using rm command:
$ sudo rm -rf /etc/mysql/

Understanding apt-get command options

• --purge : Remove given packages and config files.
• remove : Uninstall packages.
• autoremove : Force to remove packages that were automatically installed to satisfy dependencies for other packages and are now no longer needed.

You have configured your MySql replication, next step is to perform maintenance and monitor your replication. Percona Toolkit for MySQL is a collection of advanced command-line tools to perform a variety of MySQL server and system tasks.

The Percona Toolkit allows you to amongst many tasks to verify MySQL replication integrity, efficiently archive rows, find duplicate indexes, summarize MySQL servers, analyze queries from logs and tcpdump, collect vital system information when problems occur.

To get started you need to install Percona Toolkit, I’m using Ubuntu as an OS on my servers, installing the percona toolkit was straight forward

apt-get install percona-toolkit

To get a summary of your databases use the command – pt-mysql-summary

pt-mysql-summary --u=username --p=password

Next you would want to setup a heartbeat table in your database so you can Monitor MySQL replication delay – for that you will use the pt-heartbeat command.

pt-heartbeat -D wpslavedb --create-table --ask-pass --check --master-server-id 1

You can find the manual for the options here.

pt-heartbeat measures replication lag on a MySQL or PostgreSQL server. You can use it to update a master or monitor a replica. mk-heartbeat depends only on the heartbeat record being replicated to the slave, so it works regardless of the replication mechanism. It works at any depth in the replication hierarchy; for example, it will reliably report how far a slave lags its master’s master’s master.

Start daemonized process to update test.heartbeat table on master:

  pt-heartbeat -D wpslavedb --update -h master-server --daemonize --ask-pass

Monitor replication lag on slave:

  pt-heartbeat -D wpslavedb --monitor -h slave-server --ask-pass
  pt-heartbeat -D wpslavedb --monitor -h slave-server --dbi-driver Pg --ask-pass

Check slave lag once and exit (using optional DSN to specify slave host):

  pt-heartbeat -D wpslavedb --check h=slave-server --ask-pass

If the replication hierarchy is “master -> slave1 -> slave2” with corresponding server IDs 1, 2 and 3, you can:

  pt-heartbeat --daemonize -D wpslavedb --update -h master --ask-pass
  pt-heartbeat --daemonize -D wpslavedb --update -h slave1 --ask-pass

Then check (or monitor) the replication delay from master to slave2:

  pt-heartbeat -D wpslavedb --master-server-id 1 --check slave2 --ask-pass

Or check the replication delay from slave1 to slave2:

  pt-heartbeat -D wpslavedb --master-server-id 2 --check slave2 --ask-pass

if you developing and writing SQL statements, this command is very useful pt-query-digest – Analyze MySQL queries from logs, processlist, and tcpdump

  pt-query-digest slow.log    // requires you to have slow query logged enabled

There are other tools Percona Toolkit, these that I shown is what I find useful for my monitoring and maintenance.

If you want to find out the best MySQL configuration for your application, you can head over to Percona’s website they have a MySql wizards.

Source: torbjornzetterlund.com