Monitoring the MySQL Server

9.17.1 Problem

You want to find out how the server was configured or monitor its state.

9.17.2 Solution

SHOW VARIABLES and SHOW STATUS are useful for this.

9.17.3 Discussion

The SHOW VARIABLES and SHOW STATUS statements provide server configuration and performance information:

mysql> SHOW VARIABLES;
+---------------------------------+-------------------+
| Variable_name | Value |
+---------------------------------+-------------------+
| back_log | 50 |
| basedir | /usr/local/mysql/ |
| bdb_cache_size | 8388600 |
| bdb_log_buffer_size | 0 |
| bdb_home | |
...
mysql> SHOW STATUS;
+--------------------------+----------+
| Variable_name | Value |
+--------------------------+----------+
| Aborted_clients | 319 |
| Aborted_connects | 22 |
| Bytes_received | 32085033 |
| Bytes_sent | 26379272 |
| Connections | 65684 |
...

This information can be useful for writing administrative applications. For example, you might write a long-running program that probes the server periodically to monitor its activity. A simple application of this type might ask the server to report the number of connections it's received and its uptime, to determine a running display of average connection activity. The queries to obtain this information are:

SHOW STATUS LIKE 'Connections';
SHOW STATUS LIKE 'Uptime';

If you want to avoid having to reconnect each time you issue the queries, you can ask the server for its client timeout period and probe it at intervals shorter than that value. You can get the timeout value (in seconds) with this query:

SHOW VARIABLES LIKE 'wait_timeout';

The default value is 28800 (8 hours), but it may be different on your system.

The MySQL Uncertainty Principle

Heisenberg's uncertainty principle for measurement of quantum phenomena has a MySQL analog. If you monitor MySQL's status to see how it changes over time, you may notice a curious effect for some of the indicators: Each time you take a measurement, you change the value you're measuring! For example, you can determine the number of queries the server has received by using the following statement:

SHOW STATUS LIKE 'Questions'

However, that statement is itself a query, so each time you issue it, you cause the Questions value to change. In effect, your performance assessment instrument contaminates its own measurements, something you may want to take into account.

Using the mysql Client Program

Writing MySQL-Based Programs

Record Selection Techniques

Working with Strings

Working with Dates and Times

Sorting Query Results

Generating Summaries

Modifying Tables with ALTER TABLE

Obtaining and Using Metadata

Importing and Exporting Data

Generating and Using Sequences

Using Multiple Tables

Statistical Techniques

Handling Duplicates

Performing Transactions

Introduction to MySQL on the Web

Incorporating Query Resultsinto Web Pages

Processing Web Input with MySQL

Using MySQL-Based Web Session Management

Appendix A. Obtaining MySQL Software

Appendix B. JSP and Tomcat Primer

Appendix C. References



MySQL Cookbook
MySQL Cookbook
ISBN: 059652708X
EAN: 2147483647
Year: 2005
Pages: 412
Authors: Paul DuBois

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