Hmm..I'm not sure that collapsed_forwarding plugin is deprecated. The plugin
in fact is based on the settings you mentioned below and allows to block
multiple parallel requests for the same object from leaking upstream.
Using the settings alone, without the plugin would not actually achieve any
request coalescing for cache miss scenarios -- it'd simply result in returning
an error back to the client. Is that what you meant by "seeing request
coalescing"? Or is your use case, not involving cache misses, but, stale cache
(e.g VOD)?
records.config — Apache Traffic Server 6.2.1 documentation
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| |
records.config — Apache Traffic Server 6.2.1 documentation
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- proxy.config.http.cache.open_write_fail_action
| Scope: | CONFIG |
| Type: | INT |
| Default: | 0 |
| Reloadable: | Yes |
| Overridable: | Yes |
This setting indicates the action taken on failing to obtain the cache open
write lock on either a cache miss or a cache hit stale. This typically happens
when there is more than one request to the same cache object simultaneously.
During such a scenario, all but one (which goes to the origin) request is
served either a stale copy or an error depending on this setting.
- 0 = default, disable cache and goto origin server
- 1 = return a 502 error on a cache miss
- 2 = serve stale if object’s age is under
proxy.config.http.cache.max_stale_age, else go to origin server
- 3 = return a 502 error on a cache miss or serve stale on a cache
revalidate if object’s age is under proxy.config.http.cache.max_stale_age, else
go to origin server
- 4 = return a 502 error on either a cache miss or on a revalidation
Thanks,
Sudheer
On Thursday, March 8, 2018, 8:58:46 AM PST, Dunkin, Nick
<[email protected]> wrote:
HI Sudheer,
Thanks for the reply. I couldn’t think of any reason either, but I wanted to
check with the community.
Just for clarification. We’re not using the Collapsed-Forwarding plugin
explicitly, I understood that that plugin was deprecated in favor of the three
configuration areas I mentioned:
- Read While Writer
- Open Read Retry Timeout
- Open Write Fail Action
We certainly don’t have the Collapsed-Forwarding plugin in the plugin.config
and we are seeing request coalescing.
Thanks,
Nick
From: Sudheer Vinukonda <[email protected]>
Reply-To: "[email protected]" <[email protected]>
Date: Thursday, March 8, 2018 at 11:49 AM
To: "[email protected]" <[email protected]>
Subject: Re: Parent.config and thundering herd.
I haven’t looked at parent proxy setup much, but at a high level, I can’t think
of any reason why an origin failover mechanism would impact request coalescing
using collapsed forwarding plugin. The open write fail action works based on
the cache key for the object and as long as that doesn’t change, it shouldn’t
matter which origin it is pulled from. As a matter of fact, we have had origin
failover setup using a custom plugin as well as request coalescing enabled in
our HLS delivery servers and didn’t see any problems with it.
Is it possible the access failures are resulting in preventing the object from
being downloaded or being cached somehow? If the object is never cached, then
you will see problems with request coalescing.
Thanks,
Sudheer
On Mar 8, 2018, at 7:25 AM, Dunkin, Nick <[email protected]> wrote:
Hi,
We’ve been using the Thundering Herd protection provided by Read While Writer,
Open Read Retry Timeout and Open Write Fail Action and have been getting some
great results. However the behavior seems to change when we start
usingparent.config in order to provide some simple origin failover (I.e simple
Primary/Secondary Origin kind of thing). My initial tests are showing multiple
access failures and not very much in the way of request coalescing.
I don’t all have the details with me now, but at a high level, should we expect
Read While Writer, Open Read Retry Timeout and Open Write Fail Action to all
work in the same way when proxy.config.http.parent_proxy_routing_enableis
enabled and we have a simple Primary/Secondary Origin configured with
"parent_is_proxy=false”? Especially when most of the time the Primary Origin
will be up and available. Are there any gotchas we should be aware of?
All this testing is with ATS 7.0 currently.
Thanks for your insight.
Nick
Nick Dunkin
Principal Engineer
o: 678.258.4071
e: [email protected]
4375 River Green Pkwy # 100, Duluth, GA 30096, USA
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