nsqd: fix ephemeral channel sub live lock #1314
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ploxiln
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Jan 3, 2021
ploxiln
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Jan 3, 2021
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@ploxiln review this if you're reviewing things 😏 |
ploxiln
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Mar 28, 2021
| } | ||
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| if (channel.ephemeral && channel.Exiting()) || (topic.ephemeral && topic.Exiting()) { | ||
| channel.RemoveClient(client.ID) | ||
| time.Sleep(1 * time.Millisecond) | ||
| continue | ||
| if i < 2 { |
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only two attempts ... could do a couple more to be "safe" ... but ephemeral channel clients can retry too, and already give up guarantees. ok, makes sense
ploxiln
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Mar 28, 2021
| return nil, protocol.NewFatalClientErr(nil, "E_TOO_MANY_CHANNEL_CONSUMERS", | ||
| fmt.Sprintf("channel consumers for %s:%s exceeds limit of %d", | ||
| topicName, channelName, p.nsqd.getOpts().MaxChannelConsumers)) | ||
| return nil, protocol.NewFatalClientErr(err, "E_SUB_FAILED", "SUB failed "+err.Error()) |
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hmm, now this is where the exiting will be checked, and we won't retry for ephemeral channels exiting as intended
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I think that's fine, if we looked up a channel that is indeed exiting we want this to fail here.
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@jehiah last chance before I land this 😏 |
jehiah
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Fixes #1251
I noticed a few things while debugging this...
The reproducible steps from #1251 caused file descriptor exhaustion in
nsqdon my macOS laptop (default configuration) The stacktrace fromnsqdconfirmed what had previously been reported, a ton of contention onnsqd.RWMutex, but I noticed this in particular:This was the goroutine ultimately holding the lock. We don't need to be persisting metadata for ephemeral topics/channels, so after changing that it "fixed" the issue in my testing. It would still be possible to construct a pathological test to cause this, so I additionally limited the retry loop and increased the timeout (which, IMO, is the "correct" behavior here anyway).
I fixed a few other things while debugging...