What is JMeter ?

What is Jmeter ? And Why to use it?

An open source tool used for knowing how efficiently a web server works or how many concurrent requests can a web server handle.

Apache JMeter may be used to test functional and performance both on static and dynamic resources (files, Servlets, Perl scripts, Java Objects, Data Bases and Queries, FTP Servers and more). It can be used to simulate a heavy load on a server, network or object to test its strength or to analyze overall performance under different load types. You can also use it perform a functional test on websites, databases, LDAPs, webservices etc.

Let us discuss few scenarios that could be tested using Jmeter, might it would help in understanding what could be done using Jmeter.

Scenario A:

You need to have a performance test of a static website http://www.abc.com for around 200 users.

Scenario B:

You need to have a performance test of a session based web product. Where user login into account, use product features, buy products, or do other activities according to product feasibility and then get logout.

Scenario C:

You need to test a token based web product with  assertion test cases or any other logical part.

Scenario D:

You need to test web product with multiple group of users that login within a ramp up period and have different accessing road map of product.

Few terminology that will be needed while measuring Jmeter output:

• Elapsed time. JMeter measures the elapsed time from just before sending the request to just after the last response has been received. JMeter does not include the time needed to render the response, nor does JMeter process any client code, for example Javascript.  
• Latency. JMeter measures the latency from just before sending the request to just after the first response has been received. Thus the time includes all the processing needed to assemble the request as well as assembling the first part of the response, which in general will be longer than one byte. Protocol analysers (such as Wireshark) measure the time when bytes are actually sent/received over the interface. The JMeter time should be closer to that which is experienced by a browser or other application client.
  
• Connect Time. JMeter measures the time it took to establish the connection, including SSL handshake. Note that connect time is not automatically subtracted from latency. In case of connection error, the metric will be equal to the time it took to face the error, for example in case of Timeout, it should be equal to connection timeout. 
• Median is a number which divides the samples into two equal halves. Half of the samples are smaller than the median, and half are larger. [Some samples may equal the median.] This is a standard statistical measure. See, for example: Median entry at Wikipedia. The Median is the same as the 50^th Percentile  
• Standard Deviation is a measure of the variability of a data set. This is a standard statistical measure. See, for example: Standard Deviation entry at Wikipedia. JMeter calculates the population standard deviation (e.g. STDEVP function in spreadsheets), not the sample standard deviation (e.g. STDEV). 
• Throughput is calculated as requests/unit of time. The time is calculated from the start of the first sample to the end of the last sample. This includes any intervals between samples, as it is supposed to represent the load on the server.
  The formula is: Throughput = (number of requests) / (total time).