DbMon Sample Collector
Many databases provide performance counters accessible via sql. DbMon lets you plot these values over time when the test is running. The plugin can also plot other values that is accessible via sql.
This screenshot show the plugin when it is used to plot read and write transactions for a SQLServer
First you need to add a "JDBC Connection Configuration" this configuration will be used to connect to the database.
Next step is to add a "jp@gc - DbMon Samples Collector" this can be found in the listeners section. Here you can add multiple lines that will be displayed in the same graph. For each line you have to configure which JDBC configuration to use, what label it should have and a SQL query that will be used.
The sql query should return a single row with a single column and that value should be a number.
This query is by default invoked once every second so it can not be to expencive. To change how often the a sample should be taken set the parameter "jmeterPlugin.dbmon.interval" to the interval in milliseconds.
Non GUI Mode
If you run JMeter in non GUI mode and want to save dbmon data to file, just configure result file saving in GUI as you do with other listeners. After running the test you may load saved file into GUI and see the values timeline.