Hi,

I didn't create a PR yet, here is a link to the issue - https://github.com/389ds/389-ds-base/issues/4812

Thanks

On Wed, Nov 24, 2021 at 10:40 PM William Brown <william.brown@suse.com> wrote:


> On 24 Nov 2021, at 22:03, James Chapman <jachapma@redhat.com> wrote:
>
>
>
> On Tue, Nov 23, 2021 at 10:22 PM William Brown <william.brown@suse.com> wrote:
>
>
> > On 23 Nov 2021, at 23:40, James Chapman <jachapma@redhat.com> wrote:
> >
> > I have done some work on 389 ds connection management that I would appreciate the community's feedback on, you can find attached a draft patch for review.
> >
> > Problem statement
> > Currently the connection table (CT) contains an array of established connections that are monitored for activity by a single process. As the number of established connections increase, so too does the overhead of monitoring these connections. The single process that monitors established connections for activity becomes a bottleneck, limiting the ability of the server to handle new connections.
> >
> > Solution
> > One solution to this problem is to segment the CT into smaller portions, with each portion having a dedicated thread to monitor its connections. But, rather than divide the CT into smaller portions, the approach I prefered was to add multiple active lists to the CT, where each active list would have its own dedicated thread.
> >
> > Benefit
> > With a single thread monitoring each CT active list, connections can be monitored in parallel, removing the bottleneck mentioned above.
> > Instead of a single CT active list containing all established connections, there will be multiple CT active lists that share the total number of established connections between them.
> > With this change I noticed a ~20% increase in the number of connections per second the server can handle.
>
> This is good, it really does help us here. It would be better to move to epoll but I think that would be too invasive and hard for the current connection code, as it would basically be a rewrite.
>
> I did try epoll() a while ago, just to see if it performs better than PR_Poll(), but I ran into some issue with permissions of file descriptors, so I ditched it.
>
> But the multiple active lists I think is a much simpler idea, especially given we can only have a single accept() anyway.
>
> Could it also be worth changing how we monitor connections? Rather than iterating over the CT, we have a connection on a "state" change issue that update to a channel, and then the monitor thread aggregates all that info together to get a snapshot of the current connection state?
>
> Yes, I can look into this.

Happy to review that too :)

>
> >
> > Opens
> > I tested this change with 100, 500, 1k, 5k and 10k concurrent connections, I have found that having two CT active lists is the optimal config. I think we should hardcode the CT active list number to two and have it hidden from the user/sysadmin, or would it be better as a configurable parameter?
>
> Hardcode. Every single tunable setting is something that we then have to support til the heat death of the universe because we have no way to "remove" support for anything. In most cases no one will ever change, nor will they know the impact of changing it to the same level we do.
>
> See also - research that literally says most tunables go unused:
>
> https://experts.illinois.edu/en/publications/hey-you-have-given-me-too-many-knobs-understanding-and-dealing-wi
>
> That makes sense alright.
> 
> I'll review the code further later, but it is worth making this a PR instead?
> Sure, I will harden the patch a bit and create a PR.

No problem mate, great work :)

>
> Thanks for your feedback
>
> >
> > Thanks
> > Jamie
> > <connection-table-multi-lists.patch>_______________________________________________
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> --
> Sincerely,
>
> William Brown
>
> Senior Software Engineer, Identity and Access Management
> SUSE Labs, Australia
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--
Sincerely,

William Brown

Senior Software Engineer, Identity and Access Management
SUSE Labs, Australia
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