Open Stack

Hi,

Continuous tracing is a cool story, but before proceeding it would be good
to estimate the overhead. There will be an additional delay introduced by
OSProfiler library itself and delay caused by events transfer to consumer.
OSProfiler overhead is critical to minimize. E.g. VM creation produces >1k
events, which gives almost 2 times performance penalty in DevStack. Would
be definitely nice to have the same test run on real environment --
something that Performance Team could help with.

Transfer part of delay can be reduced by e.g. writing events to local file
and then processing them with Logstash + Grok. Agent-based approach is good
for more real-time processing -- can we consider to use Logstash UDP [1]
input or Elastic Beat [2] framework? OSProfiler has drivers support (works
in Pike!) and we can give operators freedom to choose the pipeline they
prefer.

[1] https://www.elastic.co/guide/en/logstash/current/plugins-inputs-udp.html
[2]
https://www.elastic.co/guide/en/beats/libbeat/current/beats-reference.html

Best regards,
Ilya Shakhat


2017-08-04 4:04 GMT+02:00 vinhnt at vn.fujitsu.com <vinhnt at vn.fujitsu.com>:

> 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> 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>
> 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> 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>
> 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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