GVP How is cache handled?

[Gui75]

Hi All,

I have a couple of questions regarding cache handling by GVP.
Documentation seems to be a bit contradictory.

1. Does it still have a sense to use external caching box?
If I read GVP deployment guide, they say :
[quote]The benefit of having an external caching server is, for example, if you have a site with ten GVP servers and an audio file expires, each server must go fetch a new copy of the audio file once it expires. If there is an external cache server, fetching a new copy of the audio file occurs only once.[/quote]
Well with external caching I think that the 10 GVP Servers will still fetch audio files once it expires.
Do they mean that the Voice web Application Server will be fetched only once (by the cache server), relieving some CPU load on it.
If so, is it advisable to combine internal caching with external caching
a.to avoid IPCS to fetch audio files each time from cache server
b. having less CPU load on Voice web Application Server when audio files are refreshed?

2. Does cache works only when fetchs fails?
According to GVP Deployment guide, in Page Collector Provisionning, when HTTP caching = on,
[quote]RFC 2616 HTTP 1.1 specification [is used] to determine whether the cached entry should be
returned to the client, or whether it should be sent to the web server[/quote]
Which is contradictory with description of "Host Cache List" parameter which says
[quote]The cached files are used only if the network fetch fails.[/quote]
Who is right?
Do I have to configure VWAP in "Host Cache List" to have the cache working for audio files?

3. Supposing that cache uses standard http mechanisms, can anyone confirm that it works the following way :
Expiration validity is set at Web Server level, ex with IIS you set at web directory level the fact that the audio files expire after one day for example
After one day, supposing audio files were not changed, how does VXML client handle expiration :
a/ will VXML client fetch audio file again
b/ or will it send a request with If-Modified-Since header which will allows server to tell that the content was not changed so that VXML client will still use file in cache?

4. If you use max-age attribute in VXML page, how does it interfere with max-age set at web server side?

5. What is the use-case for using max-stale in a VXML page?


Thanks for your answers, I think that if I have them all, I could do some white paper and have a chance to win the 500 dollars


By the way I had a look at tutorial about GVP 7.2 cache, but it changed since and lot of it is unclear

[cavagnaro]

Hum, will try to help a little bit. In HTML world we have two ways of cache. On client side (our browsers) and in web servers.

Lets imagine we create a web page (index.asp) where we see the sum of a and b where these values where read from a DB initially a=2 and b=2, then we go to (modify.asp) and we say that now a=4, and return to index.asp, with local cache = on, what our browsers will do is, like they already visited the same web page few seconds ago, it will not go to the web server to pull it again, instead will load it from local cache (temp folder) and will print out again a=2 and b=2...so we as programmers will need to disable the local cache so the change of a=4 will be shown as the browser will go again to the web server to pull the data.
This is good for dynamic pages, however for pages that are not dynamic cache=on is great because will reduce bandwidth and increase speed. The same applies for vxml as the browser is our phone now only and the web server will build the cache for them.

When we have a proxy, external cache, what happens is as documentation mentions, the first server that request the audio file will trigger the cache, then when the other 9 servers do the same, proxy will already have the audio file and will not need to go the MRCP server again. So only 1 request was needed instead of 10 going directly to the MRCP server.

Don't confuse the end user cache with web server cache, which are similar but functionalities are quiet different.

Hope it helps somehow.

[Gui75]

Thanks Cavagnaro,

Let's try to summarize what you said and tell me please if I am wrong :
a. Cache is not used for dynamic pages (fortunately as shown by your example)
b. External cache can lower load on MRCP Server (TTS or ASR) or VWAS avoiding requests to it

I still have doubts about "Host Cache List " parameter of Page Collector provisionning :
- does it take as a value urls from VWAS, MRCP Servers and perhaps also Dispenser
- why does doc says that the cached files are used only if the network fetch fails.

I still wonder if it has a sense to use both External caching and Internal Caching
If I only use external caching, I think that the load on IPCS will be higher because he will request audio each time (unless if-modified-since header allows to avoid downloading audio files again). If I only use internal caching load will be higher on MRCP Server and VWAS...

Finally of course, I am interested by your answers on 3., 4. and 5.

Regards,