Open Stack

On 05/22/2017 05:39 AM, Matthew Booth wrote:
> 
> There are also a couple of optimisations to make which I won't bother 
> with up front. Dan suggested in his CellsV2 talk that we would only 
> query cells where the user actually has instances. If we find users tend 
> to clump in a small number of cells this would be a significant 
> optimisation, although the overhead on the api node for a query 
> returning no rows is probably very little. Also, I think you mentioned 
> that there's an option to tell SQLA not to batch-process rows, but that 
> it is less efficient for total throughput? I suspect there would be a 
> point at which we'd want that. 

it's the yield_per() option and I think you should use it up front, just 
so it's there and we can hit any issues it might cause (shouldn't be any 
provided no eager loading is used).  Have it yield on about 5 rows at a 
time.  The pymysql driver these days I think does not actually buffer 
the rows but 50 is very little anyway.




If there's a reasonable way to calculate
> a tipping point, that might give us some additional life.
> 
> Bear in mind that the principal advantages to not using Searchlight are:
> 
> * It is simpler to implement
> * It is simpler to manage
> * It will return accurate results
> 
> Following the principal of 'as simple as possible, but no simpler', I 
> think there's enormous benefit to this much simpler approach for anybody 
> who doesn't need a more complex approach. However, while it reduces the 
> urgency of something like the Searchlight solution, I expect there are 
> going to be deployments which need that.
> 
> 
>         More over, during the query there are instances operation(
>         create, delete)  in parallel during the pagination/sort query,
>         there is situation some cells may not provide response in time,
>         or network connection broken, etc, many abnormal cases may
>         happen. How to deal with some of cells abnormal query response
>         is also one great factor to be considered.
> 
> 
> Aside: For a query operation, what's the better user experience when a 
> single cell is failing:
> 
> 1. The whole query fails.
> 2. The user gets incomplete results.
> 
> Either of these are simple to implement. Incomplete results would also 
> additionally be logged as an ERROR, but I can't think of any way to also 
> return to the user that there's a problem with the data we returned 
> without throwing an error.
> 
> Thoughts?
> 
> Matt
> 
> 
>         It's not good idea to support pagination and sort at the same
>         time (may not provide exactly the result end user want) if
>         searchlight should not be integrated.
> 
>         In fact in Tricircle, when query ports from neutron where
>         tricircle central plugin is installed, the tricircle central
>         plugin do the similar cross local Neutron ports query, and not
>         support pagination/sort together.
> 
>         Best Regards
>         Chaoyi Huang (joehuang)
> 
>         ________________________________________
>         From: Matt Riedemann [mriedemos at gmail.com
>         <mailto:mriedemos at gmail.com>]
>         Sent: 19 May 2017 5:21
>         To: openstack-dev at lists.openstack.org
>         <mailto:openstack-dev at lists.openstack.org>
>         Subject: [openstack-dev] [nova] Boston Forum session recap -
>         searchlight        integration
> 
>         Hi everyone,
> 
>         After previous summits where we had vertical tracks for Nova
>         sessions I
>         would provide a recap for each session.
> 
>         The Forum in Boston was a bit different, so here I'm only
>         attempting to
>         recap the Forum sessions that I ran. Dan Smith led a session on
>         Cells
>         v2, John Garbutt led several sessions on the VM and Baremetal
>         platform
>         concept, and Sean Dague led sessions on hierarchical quotas and API
>         microversions, and I'm going to leave recaps for those sessions
>         to them.
> 
>         I'll do these one at a time in separate emails.
> 
> 
>         Using Searchlight to list instances across cells in nova-api
>         ------------------------------------------------------------
> 
>         The etherpad for this session is here [1]. The goal for this
>         session was
>         to explain the problem and proposed plan from the spec [2] to the
>         operators in the room and get feedback.
> 
>         Polling the room we found that not many people are deploying
>         Searchlight
>         but most everyone was using ElasticSearch.
> 
>         An immediate concern that came up was the complexity involved with
>         integrating Searchlight, especially around issues with latency
>         for state
>         changes and questioning how this does not redo the top-level
>         cells v1
>         sync issue. It admittedly does to an extent, but we don't have
>         all of
>         the weird side code paths with cells v1 and it should be
>         self-healing.
>         Kris Lindgren noted that the instance.usage.exists periodic
>         notification
>         from the computes hammers their notification bus; we suggested
>         he report
>         a bug so we can fix that.
> 
>         It was also noted that if data is corrupted in ElasticSearch or
>         is out
>         of sync, you could re-sync that from nova to searchlight, however,
>         searchlight syncs up with nova via the compute REST API, which
>         if the
>         compute REST API is using searchlight in the backend, you end up
>         getting
>         into an infinite loop of broken. This could probably be fixed with
>         bypass query options in the compute API, but it's not a fun problem.
> 
>         It was also suggested that we store a minimal set of data about
>         instances in the top-level nova API database's instance_mappings
>         table,
>         where all we have today is the uuid. Anything that is set in the API
>         would probably be OK for this, but operators in the room noted
>         that they
>         frequently need to filter instances by an IP, which is set in the
>         compute. So this option turns into a slippery slope, and is
>         potentially
>         not inter-operable across clouds.
> 
>         Matt Booth is also skeptical that we can't have a multi-cell query
>         perform well, and he's proposed a POC here [3]. If that works
>         out, then
>         it defeats the main purpose for using Searchlight for listing
>         instances
>         in the compute API.
> 
>         Since sorting instances across cells is the main issue, it was also
>         suggested that we allow a config option to disable sorting in
>         the API.
>         It was stated this would be without a microversion, and
>         filtering/paging
>         would still be supported. I'm personally skeptical about how
>         this could
>         be consider inter-operable or discoverable for API users, and
>         would need
>         more thought and input from users like Monty Taylor and Clark
>         Boylan.
> 
>         Next steps are going to be fleshing out Matt Booth's POC for
>         efficiently
>         listing instances across cells. I think we can still continue
>         working on
>         the versioned notifications changes we're making for searchlight as
>         those are useful on their own. And we should still work on enabling
>         searchlight in the nova-next CI job so we can get an idea for
>         how the
>         versioned notifications are working by a consumer. However, any
>         major
>         development for actually integrating searchlight into Nova is
>         probably
>         on hold at the moment until we know how Matt's POC works.
> 
>         [1]
>         https://etherpad.openstack.org/p/BOS-forum-using-searchlight-to-list-instances
>         <https://etherpad.openstack.org/p/BOS-forum-using-searchlight-to-list-instances>
>         [2]
>         https://specs.openstack.org/openstack/nova-specs/specs/pike/approved/list-instances-using-searchlight.html
>         <https://specs.openstack.org/openstack/nova-specs/specs/pike/approved/list-instances-using-searchlight.html>
>         [3] https://review.openstack.org/#/c/463618/
>         <https://review.openstack.org/#/c/463618/>
> 
>         --
> 
>         Thanks,
> 
>         Matt
> 
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> 
> 
> -- 
> Matthew Booth
> Red Hat Engineering, Virtualisation Team
> 
> Phone: +442070094448 (UK)
> 
> 
> 
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