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Manual Chapter: Administrator Guide for the BIG-IP WebAccelerator Module: Glossary
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acceleration policy

An acceleration policy is a collection of rules that determine how the WebAccelerator system caches, assembles, and responds to HTTP requests. See the Policy Management Guide for the BIG-IP WebAccelerator Module for more information about acceleration policies.

application profile

An application profile provides the key information that the WebAccelerator system needs to appropriately handle requests to the applications on your site, and consists of a host map and a specified acceleration policy.


Assembly is the process of running a compiled response in order to respond to an HTTP request. When the WebAccelerator system receives an HTTP request that it can service from its cache, it places that request on an assembly queue. The WebAccelerator system then uses special threads to run the compiled response (including any related ESI-compiled response) and assembles the content required to respond to the request. See also Edge Side Includes.

change logs

Change logs contain information about page requests. The WebAccelerator system buffers change log information in memory until the specified threshold is reached. Once the threshold is reached, the WebAccelerator system writes the information to the hard drive.

compile queue

When the WebAccelerator system sends a request to the origin servers and receives a response, it compiles that response into an internal format. The WebAccelerator system then uses the compiled response object to assemble responses for the client. To perform compilation, the WebAccelerator system uses a compile queue or an ESI compile queue (if the compiled responses contained ESI data). See also Edge Side Includes.

Configuration utility

The Configuration utility is the browser-based graphical user interface for the BIG-IP system. The Configuration utility provides you access to the WebAccelerator module, as well as the network, system, and local traffic configuration objects.

content lifetime

Content lifetime is the length of time that is allowed to elapse before the compiled responses expire and the WebAccelerator system sends a request to the origin server for fresh content. Content lifetime can vary for each compiled response.

documents group

A documents group consists of objects or files that are 20KB or larger and size and contain Microsoft Word, Microsoft Excel, and Microsoft Power Point objects, or Adobe PDF files.

Edge Side Includes

Edge Side Includes (ESI) is a simple markup language that supports web surrogates, such as the WebAccelerator system, and is used to define web page components for dynamic assembly and delivery of web applications. For more information about Edge Side Includes (ESI) see the Policy Management Guide for the BIG-IP WebAccelerator Module.

enterprise MIB files

Enterprise MIB files are MIB files that pertain to a particular company, such as F5 Networks, Inc. See also MIB files.

Express Connect

Most browsers create up to two persistent TCP connections for each domain from which they are requesting data. The WebAccelerator system provides an option called Express Connect that modifies embedded URLs with unique subdomains, which prompts the browser to open more persistent connections (up to two per subdomain generated by the WebAccelerator system). These connections browsers result in faster data downloads.


The WebAccelerator system uses a shell script called hds_prune to clear compiled responses that are no longer needed from the WebAccelerator system's on-disk cache. The script works by periodically checking the current capacity of the on-disk cache. If the amount of available free space for the on-disk cache is less than, or equal to, the minimum amount that you specified, the script prunes the cache. In doing so, the script removes enough data from the on-disk cache to satisfy the maximum amount that you specified. That is, when the script is done, the amount of free space in the on-disk cache partition is as big as the maximum you set.

hit logs

Hit logs contain the same type of information as in the web server log files. The WebAccelerator system buffers hit log information in memory until the specified threshold is reached. Once the threshold is reached, the WebAccelerator system writes the information to the hard drive.

host map

A host map is defined for each application profile and contains a list of hosts to which the Web Accelerator system can match HTTP requests. See also application profile.


A MIB, presented in a hierarchal tree structure, defines the standard objects that you can manage for a device.

MIB files

MIB files specify values for the data objects defined in the MIB. This set of MIB files consists of standard SNMP MIB files and enterprise MIB files. See also enterprise MIB files.

object ID (OID)

Each object defined in the MIB has a unique OID, written as a series of integers. The OID indicates the location of the object within the MIB tree.

origin servers

Most sites are built on a collection of web servers, application servers, and database servers that we refer to collectively as origin servers. Origin servers can serve all possible permutations of the content offered by your site, while the WebAccelerator system only stores and serves page content combinations that were previously requested by clients visiting your site.


When the WebAccelerator system meets the maximum limit for in-memory cache, it removes (or pops) cached objects that have not been accessed for the longest period of time.

Rewrite Engine

The Rewrite Engine consists of a procedural language for writing custom response rewrite scripts to manipulate HTTP responses received from the origin servers. For information about customizing response rewrite scripts, contact your F5 Networks Consultant. See also response rewrite scripts.

response rewrite scripts

Response rewrite scripts manipulate HTTP responses that it receives from the origin servers. This manipulation occurs before the response is processed by the WebAccelerator system, so it is the manipulated response that the WebAccelerator system manages and caches, not the actual response sent by the origin servers. For information about customizing response rewrite scripts, contact your F5 Networks Consultant.

requested host

When you create a host map, you identify the domain as it appears on the HTTP HOST request header. These domains are called requested hosts. When you specify the host name for the requested host in a host map, you can use an asterisk (*) followed by a period as a wildcard for the first character in the domain. The asterisk can represent one or more subdomains. Using a wildcard enables you to map several subdomains to one origin web server in one step. This saves time if your site has many subdomains. See also host map.

Simple Network Management Protocol (SNMP)

SNMP is an industry-standard protocol that gives a standard SNMP management system the ability to remotely manage a device on the network. One of the devices that an SNMP management system can manage is a WebAccelerator system.

SNMP agent

Part of a standard SNMP implementation, an SNMP agent runs on a managed device, and fulfills requests, from an SNMP manager.

SNMP manager

Part of a standard SNMP implementation, an SNMP manager runs on a management system, and makes requests to a device.

socket tunnel

A socket tunnel is a mechanism by which you can identify traffic that the WebAccelerator system should pass on to an identified host and port. You can use socket tunnels to configure the WebAccelerator system to handle traffic, such as SSL or FTP sessions, that should not or cannot be managed by a cache.


The process that the WebAccelerator system uses for HTTP manipulation is called transforms.

Unique Content Identifier (UCI)

Origin servers generate specific responses based on certain elements in the request, such as the URI and query parameters. The WebAccelerator system uses these specific elements as part of the identifier to easily match future requests to the correct content in its cache. The WebAccelerator system uses the UCI for both the request and the compiled response that it created to service the request.

unmapped request

A request for a domain that is not listed in the requested host list is called an unmapped request. By default, the WebAccelerator system replies to clients that request unmapped hosts with an HTTP 403 response code. F5 Networks recommends that you reconcile unmapped requests by adding the host name to the host map for the applications that are using the specified application policy set.

URL normalization

When the WebAccelerator system analyzes the contents of a response, it creates an object ID based on that specific content. The WebAccelerator system then inserts the object ID into the response returns it to the client. This process, called URL normalization, enables the WebAccelerator system to recognize content independent of the URL.

Once the WebAccelerator system performs URL normalization, it can send the normalized URL in a redirect to the browser client that sent the request. The browser can use the normalized URL to search its own cache, in case it has a copy of the content that it could not recognize based on the request URL. If the browser finds the content in its cache, the WebAccelerator system does not have to send the content. This reduces bandwidth usage and speeds up the response time for the end user.

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