Load-testing terms, explained.

Glossary

Business Case

An interaction a user has with the web application that has meaning in a business context. Could be as simple as viewing a single page, or as complicated as performing an entire transaction. In WPLoadTester this represents a series of HTTP transactions repeated by virtual users during a test. Also known as a test case.

Cache

The browser keeps a copy of recently requested resources so it doesn't have to ask the server again. This is what makes a graphics-heavy site — with the same menu bars and icons on every page — feel fast after the first load.

Controller

WPLoadTester runs in two modes: as the controller or as an engine. The controller is the GUI that records, edits, and executes tests. Only one controller can run on a network per license key.

Cookie

A small piece of text (typically under 1 KB) the web server asks the browser to store. The browser sends it back on every subsequent request to that server. The most common method of session tracking.

Delay Time

Time between receipt of one URL and the request of the next. WPLoadTester records this while capturing a business case and uses it to accurately simulate user behavior during a test. Between a page and its first image, delay time is browser processing. Between the last image and the next page, it represents the user reading and deciding what to do next — that interval is called think time.

Engine

WPLoadTester can run as the controller or as an engine. In engine mode it presents a console interface and listens for commands from a controller, generating virtual users on demand. Many engines can serve one controller to generate massive load.

FTP (File Transfer Protocol)

A network protocol for sending and receiving files. FTP runs on top of TCP/IP.

HTTP (HyperText Transfer Protocol)

The protocol between web browsers and web servers for transferring pages and associated files. The language of the World Wide Web. HTTP runs on top of TCP/IP.

HTTP Transaction

A request from the browser to the server and the corresponding response, both over HTTP. This round trip lets the browser ask for a URL and get a response. It may include data the browser sends (form fields, uploaded files) and content the server returns (page, image, etc.).

Host

A computer connected to a TCP/IP network, including the Internet. Each host has a unique IP address.

IP (Internet Protocol)

A network protocol that specifies the format of data transferred between two hosts (packets, or datagrams) and the addressing scheme. IP alone is like the postal system: you can address a package and drop it in, but there's no direct link between sender and recipient. IP is normally paired with TCP.

IP Address

An identifier the IP protocol uses to identify a host. The current version, IPv4, uses four numbers (0–255) like 161.58.192.211. Some addresses have special meaning: 127.0.0.1 is the loopback address; 10.*.*.* and 192.168.*.* are reserved for internal networks.

License Key

An encrypted file containing the license information for your WPLoadTester install.

Multihome

A host connected to two or more networks, or with two or more network addresses. Often used to increase maximum throughput by giving a server multiple network interfaces.

Proxy Server

A server, typically on a private network, that allows access to external network resources. Common in corporate networks where the firewall blocks direct Internet access — the browser is configured to send requests through the proxy. All major browsers support this in a "Use a Proxy Server" config section.

Real Browser

An actual browser — exactly the same as a user would use — such as Google Chrome.

Sample Period

A time window during a load test during which data is aggregated. The statistics WPLoadTester calculates are computed per sample period.

Session Tracking

HTTP is stateless: between the time your browser gets a page and asks for the next, the server has forgotten who you are. Any application that needs to remember you (anything with a login) needs to track sessions. The most common techniques are cookies and URL rewriting.

SMTP (Simple Mail Transfer Protocol)

A network protocol for transferring email between servers. Most internet email systems use SMTP. Runs on top of TCP/IP.

TCP (Transmission Control Protocol)

A network protocol that lets two hosts establish a connection and exchange streams of data. TCP guarantees delivery and order. A little like a phone call — there's an extended connection between two hosts during which either can send data.

Test Case

See Business Case.

TCP/IP

The communications protocol suite that connects hosts on the Internet. TCP/IP combines TCP and IP to provide addressing and reliable data transfer for many other internet protocols, including HTTP, FTP, and SMTP.

Think Time

The time between the browser displaying a page and the user clicking a link to the next. This is what the user spends reading the page or deciding what to do. WPLoadTester records think time when capturing a business case and uses it to accurately simulate users during a test. See also delay time.

TTFB (Time to First Byte)

The duration between the virtual user making an HTTP request and the first byte of the response arriving. Gives a sense of network and web-server responsiveness; consists of socket connection time, request transmission time, and time to receive the first response byte.

URL (Uniform Resource Locator)

A specially formatted string describing a resource on the Internet. The browser uses this to find the resource on the network. A typical URL looks like http://www.webperformance.com/library/dictionary.html.

Virtual Browser

A simulated browser that mimics everything a real browser does — concurrent socket connections, caching behavior — without actually rendering page content. This is what lets a single machine generate thousands of virtual users efficiently.

Virtual User

A software entity, internal to WPLoadTester, that simulates a real user by repeatedly performing a business case during a load test.