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From "Madhava Gaikwad (madgaikw)" <madga...@cisco.com>
Subject RE: partial object caching
Date Thu, 06 Aug 2015 15:55:58 GMT
That’s cool Sudheer. Let me go through the code and understand if I can control the drawback
(wasting bandwidth) based on resource URL. Say for apple update download it makes sense to
download it completely so handheld devices are served well. Even resources containing pdf
etc can be served similarly.

For streaming the resources to multiple clients, I can setup varnish to do it. For video links,
again varnish should be OK, Losing videos on restarts should not be big issue as they have
lesser cache hits unless they are viral ones.

Thanks a lot for your help and inputs.
Madhava

From: Sudheer Vinukonda [mailto:sudheerv@yahoo-inc.com]
Sent: Thursday, August 06, 2015 9:14 PM
To: Madhava Gaikwad (madgaikw); users@trafficserver.apache.org
Subject: Re: partial object caching

Background Fetch<https://docs.trafficserver.apache.org/en/latest/reference/plugins/background_fetch.en.html>
plugin takes care of that issue for you and won't allow more than one download for the same
object (cache key) at a time. We use that in production (and I think/know a few other significant
deployments do as well) and don't see any issues with fd exhaustion or multiple downloads
for the same file.

The only drawback (if you can call it so) with the solution is that, you may potentially waste
bandwidth/cache space for a really large object which may not be requested by clients often.

Thanks,

Sudheer



On Thursday, August 6, 2015 8:24 AM, Madhava Gaikwad (madgaikw) <madgaikw@cisco.com<mailto:madgaikw@cisco.com>>
wrote:

Thanks Sudhir for the response. If too many clients starts doing range requests or even a
single client starts sending multiple range requests, using background fetch, may cause multiple
downloads to start, reason being downloads will not be sharable. Keeping rest of the client
connection  idle till, first download completes also not useful as it may cause FD exhaustion
for smaller footprint devices. I may be talking too much without knowing much about implementation
details.

Thank you.
Madhava

From: Sudheer Vinukonda [mailto:sudheerv@yahoo-inc.com]
Sent: Thursday, August 06, 2015 8:36 PM
To: users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>
Subject: Re: partial object caching

As of v6.0, ATS does not support Partial object caching (ala byte range caching).

However, ATS does support returning partial byte range responses if the whole object is already
cached. Background Fetch<https://docs.trafficserver.apache.org/en/latest/reference/plugins/background_fetch.en.html>
plugin takes advantage of this fact, by initiating a full object download in the background
on receiving a byte range request for an object that's not in the cache yet. Once the full
object is downloaded and populated into the cache, subsequent byte range requests are directly
served from the cache.


Thanks,

Sudheer


On Thursday, August 6, 2015 12:34 AM, Madhava Gaikwad (madgaikw) <madgaikw@cisco.com<mailto:madgaikw@cisco.com>>
wrote:

Hello experts,

I have legacy forward proxy used in enterprise network facing to internet behind firewall.
Unfortunately it cannot do partial object caching. I am looking if I can get an alternate
proxy to do this.
My requirement is:
1.       Partial object caching so updates by apple etc. can be cached. Also video caching
will just work.
2.       Streaming to multiple client at same time should be possible from single server connection.

It seems varnish can do above stuff. But it works effectively as reverse proxy, so I have
to position it before my proxy, as it cannot work as upstream proxy directly. Also its cache
seems gets vanished after restart(Everything in cache is from heap).
Do you guys know if ATS can do this functionality? I believe it is not possible, but I thought
just ask if we achieve this by any means. A pointing to how to would be really appreciated.


Thank you from Newbie,
Madhava


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