Entering a nether portal causes 100% CPU every time

This issue is still occurring on 1.20.81 

Still occurring in 1.20.81.01

@greymagic27 This does not happen outside of BDS

can confirm that

server.properties:
client-side-chunk-generation-enabled=false
 
reduce time to load nether while entering portals.
overwise, sometimes (below 50% cases) - player can hear footsteps sounds for a minute or so, and then after loading to Nether can fall down to lava through blocks below the portal.
 
So, developers, server need more time to load - just add more seconds in a process, or make some subrouting to check memory loading.
High CPU = unzipping and reading too more chunks in one moment.
 
IMO

Thanks for the report. We will take a look.

If client-side-chunk-generation-enabled isn't set to "true" in the server.properties, it can take quite a long time for CPU performance to settle if render distances are high.

If you're experiencing this, please post a comment with whether you're using client-side-chunk-generation-enabled and mention what your max render distance setting is.

For what it's worth, my 1.21.1.03 BDS has the same issue, but a perf recording during the issue period where a client is nether portaling mostly shows that the CPU "usage" is actually just threads spin-waiting on lock contention.

client-side-chunk-generation-enabled=true

for me, but it shouldn't matter greatly in this particular portaling event, the surrounding areas on both sides of the portal have been mutated and stored into the leveldb already so need to be fetched from the server anyways rather than the client generating its own.

The performance is extremely bad at all of the client view distances I tried from 24-50, and entering the nether portal takes 20-30 seconds.

edit: I spun up my world on Windows Server 2022 and it has the same issue, it's not exclusively a linux issue.

Thank you for your report!

However, this issue has been temporarily closed as Awaiting Response.

Is this issue occurring also in newly created worlds?

This ticket will automatically reopen when you reply.

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Can confirm this is still an issue in version 1.21.2.02

Something to note; this issue not only occurs in brand new worlds, but also effects both Modded and un-modded Worlds.

Further update, I enabled client-side-chunk-generation-enabled on the server that I help run, with render distance set at 20, and this actually caused a lot more issues than when it was disabled.

Not only was the nether laggy, but the overworld starting lagging more, with chunks taking anywhere up to 30 seconds to load in.

After disabling the client-side-chunk-generation-enabled, the world goes back to only lagging when players go to the nether.

To add some data from my experience:

• Newly created worlds

• Tested BDS on:

  • debian 12 LXC (12 CPU Cores)

  • ubuntu 22.04 LXC (12 CPU Cores)

  • Windows 10 VM (12 CPU Cores)

• Tested using `max-threads` set to 4, 8, 12, and 0.

In all instances, all threads use 100% CPU.

Some interesting observations:

• The greater the view distance, the longer it takes to load the Nether.

• It appears the more chunks previously generated in the Nether, the longer it takes to load.

• The more threads I assign to a world, the longer it takes to load the Nether.

• The CPU usage when navigating around the Nether (generating new chunks), is much higher than in the Overworld (when generating new chunks). 

Steps to reproduce:

1. Create new world from fresh unzip of bds server download, using the default `server.properties`.

2. Edit `server.properties` and set to creative mode, cheats enabled

3. Start server

4. Join world with Windows client set to 32 view distance

5. Back at server console, give user OP

6. Back at client, Create a portal

7. Enter portal (At this point it doesn't take too long)

8. Fly around nether to generate some chunks, in all directions away from portal.

9. Return to Overworld

10. Enter portal to Nether

Expected:

Nether should load in a few seconds

Actual:

It now takes longer to load the Nether.  

Sometimes the Nether appears, but you cannot interact with it, nor can you open your inventory.  After a while (10 - 60 seconds), you are teleported back to the portal and you can now interact with the Nether.

I can confirm this issue occurs on Windows 11 23H2 running 1.21.3 BDS with client-side-chunk-generation-enabled=true.

I also experienced that after immediately loading into the Nether, the portal, all other structures, and excavating is reverted to the original Nether landscape. After 30-60 seconds, the Nether loads with the structures and excavating, and you "teleport"/snap to the portal.

Below is a link to a video showing the lag described above.

https://youtu.be/xxw9vdYZ3Bs

Dedicated Server Specs are below.

Device name    minecraftserver
Processor    Intel(R) Core(TM) i7-9700 CPU @ 3.00GHz   3.00 GHz
Installed RAM    32.0 GB (31.8 GB usable)

Thank you for the details and the repro video! We will take a look

client-side-chunk-generation-enabled true or false cause same issue with my server i'v 3 server with same nether bug on linux centos

Having the same issue. Teleporting to the nether causes 100% CPU usage (all cores) for a good 30 seconds. The other players in the overworld experience severe lag.