Reference Guide

Zend Download Server
This component is not relevant for Windows and IBM i Servers.
Zend Server Reference Manual
The ZDS (Zend Download Server) component improves Apache's scalability by taking over static content
downloads and passing them to a dedicated process that is optimized for parallel downloads (not
supported on Windows servers).
The ZDS enhances Apache's static download capabilities. This releases Apache processes to handle
more dynamic requests. There are two ways to define which files will be serviced by the ZDS: Either via
the API or via an external configuration file (mime_types).
A single ZDS process can handle substantially more concurrent downloads, compared to Apache's
capabilities.
The Zend Download Server is a PHP extension that forks an HTTP server separate from Apache to be
used for serving large files of given types by redirecting regular requests from your Apache to a separate
server.
The Zend Download Server is a PHP extension that forks an HTTP server (separate from Apache) to
serve specific types of large files, by redirecting regular requests from your Apache to a separate server.
The Zend Download Server offloads the limited Apache process activity to avoid the situation where a
connection is open for a long time to serve large downloads, which in turn prevents the Apache from
serving requests that can be handled immediately. The concept is similar to the express lane in a
supermarket: A separate "lane" is made available for large downloads, which frees up the other lanes for
smaller downloads.
Based on the settings in the mime_types file, specific file extensions are immediately identified when the
request is received: These downloads are rerouted to a separate server.
This essentially creates a separate process which functions as an HTTP daemon, dedicated to
downloads.
The mechanism is a PHP extension that creates a daemon to handle the rerouting when the extension
loads. We also provide a mime_types file and an API for explicitly directing content (a file or buffer) to be
handled by the ZDS (in parallel to using the mime_types file, depending on your preferences).
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