Open Stack

Hi Rajul,

For the `agent idea`, I think it is very good.
However, in OpenStack, that idea may be really hard for us.
The reason is the same with what Boris think.

For the sampling part, head-based sampling can be implemented in OSprofiler.
For tail-based and adaptive sampling, it is another story.
However, in naïve way, we can use sampling abilities from other OpenTracing compatible tracers
such as Uber Jaeger, Appdash, Zipkin (has an open pull request), LighStep … by making OSprofiler
compatible with OpenTracing API.

ICYMI, Boris is father of OSprofiler in OpenStack [1]

[1] https://specs.openstack.org/openstack/oslo-specs/specs/mitaka/osprofiler-cross-service-project-profiling.html

Best regards,

Vinh Nguyen Trong
PODC – Fujitsu Vietnam Ltd.

From: Rajul Kumar [mailto:kumar.raju at husky.neu.edu]
Sent: Friday, 04 August, 2017 03:49
To: OpenStack Development Mailing List (not for usage questions) <openstack-dev at lists.openstack.org>
Subject: Re: [openstack-dev] [oslo][performance] Proposing tail-based sampling in OSProfiler

Hi Boris

That is a point of concern.
Can you please direct to any of those?

Anyways, we don't have anything in place for OpenStack yet.
Now, either we pick another tracing solution like Zipkin, Jaeger etc. which have their own limitations OR enhance OSProfiler.
We pick the later as it's most native and better coupled with OpenStack as of now.
I understand that we may be blocked by these issues. However, I feel it'll be better to fight with OSProfiler than anything else till we come up with something better :)

Thanks
Rajul



On Thu, Aug 3, 2017 at 4:01 PM, Boris Pavlovic <boris at pavlovic.me<mailto:boris at pavlovic.me>> wrote:
Rajul,

May I ask why you think so?

Exposed by OSprofiler issues are going to be really hard to fix in current OpenStack architecture.

Best regards,
Boris Pavlovic

On Thu, Aug 3, 2017 at 12:56 PM, Rajul Kumar <kumar.raju at husky.neu.edu<mailto:kumar.raju at husky.neu.edu>> wrote:
Hi Boris

Good to hear from you.
May I ask why you think so?

We do see some potential with OSProfiler for this and further objectives.

Thanks
Rajul

On Thu, Aug 3, 2017 at 3:48 PM, Boris Pavlovic <boris at pavlovic.me<mailto:boris at pavlovic.me>> wrote:
Rajul,

It makes sense! However, maybe it's a bit too late... ;)

Best regards,
Boris Pavlovic

On Thu, Aug 3, 2017 at 12:16 PM, Rajul Kumar <kumar.raju at husky.neu.edu<mailto:kumar.raju at husky.neu.edu>> wrote:
Hello everyone

I have added a blueprint on having tail-based sampling as a sampling option for continuous tracing in OSProfiler. It would be really helpful to have some thoughts, ideas, comments on this from the community.

Continuous tracing provides a good insight on how various transactions behave across in a distributed system. Currently, OpenStack doesn't have a defined solution for continuous tracing. Though, it has OSProfiler that does generates selective traces, it may not capture the occurrence. Even if we have OSProfiler running continuously [1], we need to sample the traces so as to cut down the data generated and still keep the useful info.

Head based sampling can be applied that decides initially whether a trace should be saved or not. However, it may miss out on some useful traces. I propose to have tail-based sampling [2] mechanism that makes the decision at the end of the transaction and tends to keep all the useful traces. This may require a lot of changes depending on what all type of info is required and the solution that we pick to implement it [2]. This may not affect the current working of any of the services on OpenStack as it will be off the critical path [3].

Please share your thoughts on this and what solution should be preferred in a broader OpenStack's perspective.
This is a step in the process of having an automated diagnostic solution for OpenStack cluster.

[1] https://blueprints.launchpad.net/osprofiler/+spec/osprofiler-overhead-control
[2] https://blueprints.launchpad.net/osprofiler/+spec/tail-based-coherent-sampling
[3] https://blueprints.launchpad.net/osprofiler/+spec/asynchronous-trace-collection

Thanks
Rajul Kumar


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