Prevent region compression from blocking the main thread

[nolife99]

What's your idea?

Sometimes region I/O will completely block the main thread as it's saving files. I do have C2ME OpenCL installed, I have no clue if this is the reason why, but nevertheless it would help to have it write on a background thread if possible or at least unblock the main thread.

[12:41:10] [linearreader-flush-barrier] [linearreader/WARN]: [LinearReader] Slow region save: r.-1.1.linear took 27989ms (threshold 500ms). Check disk health.
[12:41:10] [linearreader-flush-barrier] [linearreader/WARN]: [LinearReader] Slow region save: r.-1.-1.linear took 27990ms (threshold 500ms). Check disk health.
[12:41:10] [linearreader-flush-barrier] [linearreader/WARN]: [LinearReader] Slow region save: r.1.1.linear took 27989ms (threshold 500ms). Check disk health.
[12:41:10] [linearreader-flush-barrier] [linearreader/WARN]: [LinearReader] Slow region save: r.0.-1.linear took 28060ms (threshold 500ms). Check disk health.

Why should this be added?

Prevent huge stalls when regions are being written. Gameplay-wise, I'll be completely blocked from gameplay for 15 seconds or more while the regions are being saved, which is very annoying

Anything else?

Hardware:
CPU: Intel Core Ultra 7 270K Plus
SSD: Acer Predator GM7000 Heatsink 1TB

[Bugfunbug]

Thank you for letting me know, I will investigate this issue, although it might take some time but I will get it done (hopefully sooner rather than later)
I guess it probably doesn’t matter which Minecraft version you are on, but if you don’t mind telling me I’d appreciate it

[Bugfunbug]

Also was this under normal load or were you flying around with an elytra and a super high render distance or something?

[nolife99]

This was on 26.2, normal load when walking around the world, same general area

[Bugfunbug]

Ok thanks, just a few more questions after doing a bit more digging:

1. In your server.properties file, is sync-chunk-writes set to “true”? And can you set it false temporarily to see if that does anything?
2. Can you try without opencl installed?
3. Are any other mods installed besides c2me and opencl?

(Also, if you’re able to, I pushed some changes which add better diagnostic logging, if you want you could try building a new LinearReader .jar file to get the better logging)

[nolife99]

I couldn't find any server.properties file, the world is fully local. I tried with OpenCL disabled and it still continued to happen.
I did a bit of testing with your new build:

[19:29:17] [linearreader-flush-1/WARN]: [LinearReader] Slow region save: r.0.-1.linear took 11138ms (threshold 500ms). Check disk health. build=0ms compress=11106ms write=0ms sync=0ms rename=0ms (sync=false) [heap 6484/16384MB used, GC 300 collections/42543ms total (cumulative since JVM start)]
[19:34:16] [linearreader-flush-1/WARN]: [LinearReader] Slow region save: r.0.1.linear took 9252ms (threshold 500ms). Check disk health. build=0ms compress=9220ms write=0ms sync=0ms rename=0ms (sync=false) [heap 6812/16384MB used, GC 615 collections/68055ms total (cumulative since JVM start)]
[19:47:07] [linearreader-flush-1/WARN]: [LinearReader] Slow region save: r.0.-1.linear took 18622ms (threshold 500ms). Check disk health. build=0ms compress=18585ms write=0ms sync=0ms rename=0ms (sync=false) [heap 7446/16384MB used, GC 1116 collections/103394ms total (cumulative since JVM start)]
[19:56:58] [linearreader-flush-1/WARN]: [LinearReader] Slow region save: r.1.1.linear took 15811ms (threshold 500ms). Check disk health. build=0ms compress=15809ms write=0ms sync=0ms rename=0ms (sync=false) [heap 10174/16384MB used, GC 1251 collections/136240ms total (cumulative since JVM start)]
[20:03:24] [linearreader-flush-1/WARN]: [LinearReader] Slow region save: r.0.-2.linear took 13010ms (threshold 500ms). Check disk health. build=0ms compress=12961ms write=0ms sync=0ms rename=0ms (sync=false) [heap 6916/16384MB used, GC 1379 collections/162185ms total (cumulative since JVM start)]
[20:03:58] [linearreader-flush-1/WARN]: [LinearReader] Slow region save: r.-2.1.linear took 13842ms (threshold 500ms). Check disk health. build=0ms compress=13841ms write=0ms sync=0ms rename=0ms (sync=false) [heap 11022/16384MB used, GC 1436 collections/180252ms total (cumulative since JVM start)]

This is with GenZGC on a 16GB heap. I have autoRecompressEnabled = false in the config
I've changed the title to more closely match the real issue

[Bugfunbug]

Based on those logs, could you try switching to a different GC, like the default G1GC, and see if that helps?

[nolife99]

G1GC did not help, and I didnt expect it to. The zstd compression is the bottleneck here

[Bugfunbug]

Ok, if you don't mind can you build a new jar with the new code I just pushed? Hopefully then the logs will provide some more useful information

[Bugfunbug]

(I can't seem to recreate it, so I need more information from you to figure out what's wrong)