ISPPlanet Cache Review Series - InfoLibria DynaCache 220i

Dyna-Caching Services
The DynaCache runs modified BSDI. It caches HTTP 0.9 through 1.1, including HTTP streaming in the DynaCache 240. DNS and FTP caching are not yet available, but scheduled for the next release. InfoLibria does not perceive demand for News (NNTP) caching. Companion products provide value-added audio and video services: MediaMall enables distribution of streaming media (stream-casting and edge-casting), while Content Commander pre-positions large files and inserts region-specific advertising into either DynaCache or MediaMall content.

Hit-forwarding is a unique feature of the DynaCache. Caching can impact e-commerce data mining because web sites cannot maintain accurate hit counts, and all hits appear to come from the cache instead of clients. The DynaCache avoids this pitfall by forwarding "hit reports" (HTTP HEAD requests) to the origin web server for every object vended from the cache. Each report carries HTTP headers from the browser request. This enables upstream bandwidth reduction while preserving end-to-end data flow from browser client to web server. However, because reports are issued before closing the cache-to-client connection, connections stay open longer with hit forwarding enabled. InfoLibria will decouple hit forwarding from client connections in the next release, further speeding browser response.

A healthy set of configuration commands are available to control caching. Default expiration, last modified factor, max expiration, and freshness validation influence when stored objects are refreshed. Content Commander can be used with the DynaCache to pre-fetch objects before they are requested, and hit report responses help to detect stale content.

Max object size, requires expires / last modified, cookie exceptions, and dontcache parameters determine which objects get cached. Clients, web servers, or entire subnets are easily bypassed with "dontcache ip" commands. Objects identified by filename extension or URL are bypassed with "dontcache keyword" commands. For request blocking, third-party filtering (e.g., WebSense, N2H2) is planned in the next release.

Changes made to cache parameters can be applied without reboot by briefly disabling, then re-enabling, the cache. To limit service disruption, a shutdown command disables the cache only after existing connections have been closed. Cache status is disabled if "show system" displays zero hit/miss counts; we'd prefer a cache status query command.

A detailed set of cache statistics are available to facilitate fine-tuning. Summary stats quantify overall usage: bytes, connections, and HTTP requests. Miss stats can be used to refine cache effectiveness by identifying why requests could not be vended (e.g., content was not fresh or contained a no-cache pragma). Delete stats enumerate why objects have been cleared, but we'd like to see information on objects stored in the cache (e.g., number, size, age).