For the first time the #CoSocialCa Mastodon server has started to struggle just a little bit to keep up with the flow of the Fediverse.
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@virtuous_sloth @mick looks, to my eye, that one peak is ~double the other. Could there be an effect where, at each read point, it either had to run through the list of all xxx, or it had to process the list twice?
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@virtuous_sloth I see this as well and I’m not totally sure what to make of it. I suspect it’s something to do with the way that the monitoring or graphing is calculating values.
The scrape interval is 15 seconds, so it doesn’t make sense for the latency to be bouncing around so much, and in such suspiciously well-defined bands.
This banding has only shown up in relation to these recent spikes.
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@rndeon @virtuous_sloth That’s an interesting idea. It looks like within the space of 15s it decides that the latency is twice or half as bad as it was 15s prior. Could be because of some sort of duplication as you suggest.
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@mick @virtuous_sloth i don't know enough about what's being plotted to have insight, but I'm curious! Is the y axis the time a particular task spent in the queue? And over 15s, it averages over all tasks that left the queue to make a data point?
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Well, we’re not out of the woods yet.
We fell behind by less than a minute for most of the day yesterday, with some brief periods where we were slower still.
The droplet is showing no signs of stress with the increased Sidekiq threads, so I can toss a bit more hardware at the problem and see if we can reach equilibrium again.
Better would be to get a clearer picture of what’s going on here.
Maybe we need to do both of these things!
10/?
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@rndeon @virtuous_sloth The sidekiq stats here are coming from this Prometheus exporter: https://github.com/Strech/sidekiq-prometheus-exporter
The graph is showing the “sidekiq_queue_latency_seconds” gauge, which is “The number of seconds between the oldest job being pushed to the queue and the current time.”
Prometheus is configured to scrape the data from the exporter every 15 seconds, and Grafana is sampling on a 15s interval as well.
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@mick @rndeon
It looks to me like the number of queued jobs is fairly low (like 1-4 queued jobs) and the jobs are sometimes arriving as pairs or triples with very little time in between (followed by a long time for the next bunch such that the average is still below the average job run time) so the second job of the pair will necessarily jump the time up. Then when the first job of the next pair is completed the time drops. -
@mick is it my fault? I think I shared a cat picture on Caturday. (Jk, keep up the great work)
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@OldManToast the smoking gun I’ve been looking for!
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This strikes me as an issue.
We have the capacity to run 40 workers (following the change I made last week, documented earlier in this thread.)
We have fairly huge backlog of pull queue jobs.
Why aren’t we running every available worker to clear this backlog?
It might be necessary to designate some threads specifically for the pull queue in order to keep up with whatever is going on here, but I am open to suggestions.
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@mick I haven’t read the entirety of the thread, so forgive me if that’s already been covered, but have you tried defining your workers with different sequences of queues.
So you could have one service defined as
/home/mastodon/.rbenv/shims/bundle exec sidekiq -c 10 -q pull -q default -q ingress -q push -q mailers
Another as
/home/mastodon/.rbenv/shims/bundle exec sidekiq -c 10 -q default -q ingress -q push -q mailers -q pull
Etc.
That wat you would have 10 workers prioritising the pull queue, but picking up other queues when capacity is available. And another 10 workers prioritising the default queue, but picking up other queues (including pull) when capacity is available.
You could permutate this for some different combination of queue priorities.
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@michael that’s where I’m headed next I think.
I’d hoped that just increasing the number of threads for the single service would be enough, but it seems like the default queue prioritization results in a backlog and idle workers.
So dedicating a number of threads per queue seems like the next sensible step.
Thanks for the suggestion!
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@mick just to be clear, what I’d suggest is not to dedicate them, but to prioritise.
Maybe you mean the same thing, but if you set up a service with
/home/mastodon/.rbenv/shims/bundle exec sidekiq -c 10 -q pull
And another with
/home/mastodon/.rbenv/shims/bundle exec sidekiq -c 10 -q push
Then that first process will sit idle when there is nothing in the pull queue, even if the push queue might be full.
If, on the other hand, you have a service defined as
/home/mastodon/.rbenv/shims/bundle exec sidekiq -c 10 -q pull -q push
And another as
/home/mastodon/.rbenv/shims/bundle exec sidekiq -c 10 -q push -q pull
Then that first command will process the push queue, after the pull queue has been emptied. And the second one will process the pull queue after the push queue has been emptied. Thus potentially wasting fewer resources.
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@michael right, I see the distinction, and hadn’t fully grasped what you were suggesting.
Given the limited resources available on our small server this seems like an excellent idea.
I’ll play with some changes on the staging system. Thanks!
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@mick What monitoring system is that?
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@rolle Prometheus, and this sidekiq-exporter https://github.com/Strech/sidekiq-prometheus-exporter
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@mick Thanks!
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@rolle I have found it extremely useful for keeping tabs on the system.
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@michael based on this advice I've added some services that prioritize various queues and we're humming along nicely now. Thank-you!
