A variant of a cache object. This was originally created to handle the VARY mechanism but has since been used for additional purposes. All alternates of an object must be equivalent in some manner, that is they are alternate forms of the same stream. The most common example is having normal and compressed versions of the stream.

The unit of storage in the cache. All reads from the cache always read exactly one fragment. Fragments may be written in groups, but every write is always an integral number of fragments. Each fragment has a corresponding directory entry which describes its location in the cache storage.

A 128 bit value used as a fixed sized identifier for an object in the cache. This is computed from the cache key using the MD5 hashing function.

A byte sequence that is a globally unique identifier for an object in the cache. By default the URL for the object is used.

The minimal self contained unit of data in the cache. Cache objects are the stored version of equivalent content streams from an origin server. A single object can have multiple variants called alternates.

The physical storage described by a single line in storage.config.

A homogenous persistent store for the cache in a single cache span. A stripe always resides entirely on a single physical device and is treated as an undifferentiated span of bytes. This is the smallest independent unit of storage.

The bottom few bits (12 currently) of the cache ID. This is used in the cache directory for a preliminary identity check before going to disk.

A user defined unit of persistent storage for the cache. Cache volumes are defined in volume.config. A cache volume is by default spread across cache spans to increase robustness. Each section of a cache volume on a specific cache span is a cache stripe.

A callable object that contains state. These are are mechanism used by Traffic Server to implement callbacks and continued computations. Continued computations are critical to efficient processing of traffic because by avoiding any blocking operations that wait on external events. In any such case a continuation is used so that other processing can [..]