mojira.dev

Guntram Blohm

Assigned

No issues.

Reported

MC-229160 Open shulker boxes seem closed to players who log in or port in Confirmed

Comments

Can confirm in 1.20.1.

 

This is likely an issue with Simple Voice Chat, at least in some circumstances, as in Dual Iron's version.

We had that plugin enabled on our server, and faced various intermittent issues:

  • timing out when logging in, as described in this bug

  • extreme lag when operating piston machines, like 300 mspt when a 4-piston flying machine was active

  • lag spikes whenever lots of blocks changed at once, be it exploding tnt in the nether or growing 2x2 large trees

When I used Wireshark to trace the network during a player log-in, I noticed the player needing 40 seconds to load 3 MB worth of chunks. A different player, logging in at the same time at a different place, got 2.5 MB in ~ 1 second. The "slow" player did NOT have a significant number of network resends, or errors,  or full TCP window conditions; the network dump showed that the server was just sending its data very slowly.

This means the issue does not really have much to do with the render distance; it's just that a very low render distance reduces the amount of data to be sent enough to arrive in time even with the very slow transfer.

 

All of these issues disappeared when we removed the Simple Voice Chat plugin.

 

My hypothesis is that Simple Voice Chat hogs one of the netty channels, and blocks Minecraft itself when MC doesn't know the channel is busy. Which means that, as soon as MC sends a lot of chunks, or chunk updates, through this one hogged channel, it slows down a lot. As long as MC doesn't use this particular Netty channel, everything is fast.

I might be wrong; I didn't even check if SVC uses netty. The only thing I can say is all our issues disappeared once the SVC plugin was removed from the server.

 

Only now do I realize that the video doesn't show the second part of the bug report. But that one should be easy to reproduce - jump on the shulker box that's opened by the first player, but which the second player sees as closed.

 

I made a video which is unfortunately too big (15 MB) to upload here.

The video is on youtube at https://www.youtube.com/watch?v=UrBjZFDdjZc

This is on a LAN world that I had just created for this purpose, both clients are vanilla, though started by MultiMC to make it easier to get two instances running on the same computer at the same time.

 

As the F3 text is hard to read in the youtube video, I attached a screenshot that should have the F3 text readable.