[tor-bugs] #31425 [Circumvention/Snowflake]: Snowflake broker is sluggish and sometimes fails

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#31425: Snowflake broker is sluggish and sometimes fails
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 Reporter:  cohosh                   |          Owner:  (none)
     Type:  defect                   |         Status:  needs_information
 Priority:  Low                      |      Milestone:
Component:  Circumvention/Snowflake  |        Version:
 Severity:  Normal                   |     Resolution:
 Keywords:  broker                   |  Actual Points:
Parent ID:                           |         Points:
 Reviewer:                           |        Sponsor:
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Comment (by cohosh):

 Replying to [comment:10 dcf]:
 > Replying to [comment:8 cohosh]:
 > > To add to the information here, starting yesterday I've been getting
 notifications from sysmon that the snowflake broker becomes unreachable
 periodically (I received 3 notifications yesterday that unreachability
 lasted approximately 10-25 minutes.
 >
 > What reachability test does sysmon do? An HTTPS request?
 Just a simple TCP reachability test to port 443.
 >
 > I wondered if there were some pathology in the in-memory data structures
 used to store active snowflakes and clients. But the set of snowflakes
 [https://gitweb.torproject.org/pluggable-
 transports/snowflake.git/tree/broker/snowflake-heap.go?h=webext-0.0.10
 uses a priority queue] and I don't see any obvious bugs. If the problem
 were an inefficient algorithm, I'd expect to see higher CPU usage anyway.

 Another main symptom of sluggishness I was experiencing was that when I
 logged in, it took forever for me to type commands and for the commands to
 run. So for example simply running `top` was a multi-minute affair. Once I
 ran it, I was similarly seeing very low CPU and memory usage.

 So it's not just that the snowflake-broker is running slowly, it seems to
 be all other processes on that machine (or at least from what I could tell
 through an SSH connection). I even stopped the snowflake broker for a few
 minutes and that didn't help at all. The machine was still just as
 sluggish.

 When I logged in again this morning, the sluggishness seems to have
 disappeared for the moment, and I haven't gotten any sysmon notifications
 recently.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31425#comment:11>
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