Reducing redundant fetching

Streaming content can be redundantly fetched

Because clients can access live or on-demand streaming content using disparate URL forms, NetCache might fetch the identical streaming content multiple times. For example, consider the following URLs:

rtsp://mediaserver.lab.netapp.com/movie.rm

rtsp://mediaserver.lab/movie.rm

rtsp://mediaserver/movie.rm

rtsp://xxx.xxx.xxx.xxx/movie.rm

Typically, requests for each of these URLs will result in four separate requests for streaming content. These redundant fetches have the following consequences:

Additional upstream bandwidth is consumed to fetch streams that could be served by splitting a live stream or serving an on-demand stream from the cache.
Each redundant fetch for on-demand streaming content is cached independently. For example, if the content had been previously cached when rtsp://mediaserver.lab/movie.rm was requested, a subsequent request for the same content from rtsp://mediaserver/movie.rm will result in a cache miss and a new connection to the origin server.

URL normalization reduces redundant fetching

You can use the streaming URL normalization options to eliminate the redundant fetches caused by URL differences. When you enable these options, NetCache resolves streaming URLs to find the authoritative domain name. NetCache will then split or cache the content using the Fully Qualified Domain Name (FQDN). Resolving URLs to the FQDN increases the cache hit rate because disparate URLs can be resolved to the same cached content.

When to use the streaming URL normalization options

Generally, the streaming URL normalization options are most useful in intranet deployments where many URLs might not contain an FQDN.

About the Streaming URL Normalization options

The following streaming URL normalization options are available:

Ignore URL Query String
When the Ignore URL Query String option is enabled, NetCache ignores the segment of the URL string that appears after the "?" query for the purposes of deciding whether the stream should be split or served from the cache.

The original URL (with the query string) is sent to the origin server for logging and validation purposes.
Resolve IP Addresses to FQDN
When the Resolve IP Addresses to FQDN option is enabled, NetCache performs a reverse DNS lookup on the IP address and caches the content using the FQDN. Resolving the IP address to the FQDN eliminates the possibility of caching duplicate content when a host has multiple IP aliases.
Resolve Host Names to FQDN
When the Resolve host names to FQDN option is enabled, NetCache performs a DNS lookup on all streaming requests that contain nonqualified host names and resolves them to the FQDN.

Note
MMS URLs are always normalized to lowercase and have their trailing slashes (up to the first "?") removed.

Before enabling the Ignore URL Query String option

If the query string includes information used to identify content and you enable the Ignore URL Query String option, NetCache will ignore the query string and retrieve the identical stream for every user accessing a given URL. Therefore, ensure that your streaming content is not distinguished by information included in the query string.

DNS considerations for streaming URL normalization deployments

DNS lookups for URL normalization can have the following consequences:

DNS lookup latency
Because of the DNS lookup involved in finding the FQDN, the Streaming URL normalization options impose additional latency at connection time. However, the additional latency is normally offset by the improved hit rate caused by URL normalization and the performance improvements created by DNS caching.
Media player timeouts
If any of the following conditions exists, the media player will be forced to sit idle and might eventually time out while NetCache waits for a DNS response:
- No DNS server exists.
- The DNS server fails.
- The DNS query fails.