[MC-168633] Villager AI causes immense lag (adds up with large village populations)

The server is crashing often - on the order of minutes. It also is taking a very long time to execute some operations like eating, smelting, and brewing.

This is happening in a chunk that has a great deal of redstone and a great many villagers and animals. The server seems stable away from this chunk.

This world was stable with very little lag in 1.14.4. I have uploaded the world in its current state as well as its last state in 1.14.4. Link provided below. I have also uploaded a screenshot of the server system specs to the same location.

I am currently running the client from the same machine as the server.

Additional notes that may be useful:

Animals and villagers move in short steps with pauses instead of smoothly.
Golems in lava take a very long time to die, with each sound occurring with a long pause in between.
I reached an impasse trying to brew a potion. The server crashes before the slow operation can complete. Then, when the server restores, the blaze rod is used but the potion brewing starts over.
CPU utilization seems fine. Uploaded screenshot.

Link to worlds and specs:

https://drive.google.com/drive/folders/1eReWDHUW6xnNoHbHDpOvRfxoYEjmPQHM?usp=sharing

Linked issues

relates to 2

MC-217906 Large amounts of axolotls cause performance issues Resolved

MC-229365 Large amounts of goats causes performance issues Resolved

Attachments

debug-report-2019-12-23_18.33.21.zip

profile-results-2019-12-23_18.33.12.txt

Comments 16

violine1101 2019-12-23T10:52:56Z

We do not have enough information to find the cause of this issue.

Please attach the crash report found in [minecraft/crash-reports/crash-<DATE>-client.txt|https://minecrafthopper.net/help/guides/finding-minecraft-data-folder] here.
If you cannot find a crash report, please attach the full launcher log found in [minecraft/launcher_log.txt|https://minecrafthopper.net/help/guides/finding-minecraft-data-folder/].

_{This issue has been temporarily closed as}_{Awaiting Response}_{. Once the requested information has been delivered, the report will be reopened automatically.}

Quick Links:
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Dan Busenbarrick 2019-12-23T19:09:06Z

The zip files I already provided contain the entire directory containing the world. This includes many, many crash log files.

violine1101 2019-12-23T23:52:29Z

These crash reports suggest that this is caused by horrendous server lag. To find out why the server is lagging, please do the following:

While the lag occurs, please run /debug start, wait a while and then run /debug stop in order to create a debug profile. Afterwards, run /debug report.

If you do not have the permission to run these commands, open your world to LAN and enable cheats. If you're on a server, make sure that you're a server operator in order to execute these commands.

Then, please attach the profile results found in [minecraft/debug/profile-results-<DATE>.txt|https://minecrafthopper.net/help/guides/finding-minecraft-data-folder], as well as the debug report found in [minecraft/debug/debug-report-<DATE>.zip|https://minecrafthopper.net/help/guides/finding-minecraft-data-folder] here.

_{This issue has been temporarily closed as}_{Awaiting Response}_{. Once the requested information has been delivered, the report will be reopened automatically.}

Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – 📖 Game Wiki

Dan Busenbarrick 2019-12-24T00:36:03Z

Done.

violine1101 2019-12-31T00:46:46Z

Sorry for the delay.

This issue is definitely caused by the 350 villagers you have in that area – the game is not able to handle this many villagers at once. I'm unsure whether we can really track this as a bug, as this would be more of a performance improvement and is not a real bug by itself. Perhaps we even have another ticket for this already, although I couldn't find one with a quick search.

To work around this problem, you have multiple options:

Reduce the number of villagers in that area
Put them into cells (edit: without a bed, and with one villager per cell) that prevent them from pathfinding constantly
Reduce server render distance drastically
Get better server hardware

I know that these workarounds don't seem exactly too helpful, but they are the best you can do to solve the issue in the short term. I'll leave this ticket open, but as it is more of a performance issue rather than a straight up bug, don't expect this to be fixed too soon.

Your world is a great benchmark for testing lag with villagers though!

6 more comments

Dan Busenbarrick 2019-12-31T01:00:39Z

Hi,

It seems that one detail is being overlooked - that these problems are not happening with 1.14.4. In the older version, the server never crashes, running for weeks at a time, where as with 1.15.1 a crash occurs regularly after a few minutes. Also, the vastly expanded time durations for smelting, brewing, sleeping, etc. do not occur in 1.14.4. Perhaps there is an unforeseen consequence to some change that was made in the newer version? Whatever the case, the situation is that the same world is fully functional in 1.14.4 and not playable in 1.15.1.

violine1101 2019-12-31T12:22:05Z

Thanks for mentioning that, that'll probably be helpful to the devs.

Also, the crash happens because of the lag. The server just gives up because too much lag occurs. The issue is the lag, not the crash. The game is supposed to crash when it can no longer keep up with the lag.

Dan Busenbarrick 2019-12-31T22:58:49Z

Fair enough that the lag is the underlying condition for the crash. I disagree, though, that this should be labeled a performance issue. There is a very large, and almost certainly unintentional difference between 1.14.4 and 1.15.1 that is causing a world to be unusable. A change this significant between the two versions is not a difference in performance but is in fact a software defect.

Dan Busenbarrick 2019-12-31T23:12:41Z

Another point is that it seems unlikely that the lag is due to insufficient hardware resources. As shown by the performance graphs I included, the CPU utilization is not high, and there is plenty of available memory. It seems doubtful that upgrading the server machine would impact the issue significantly.

Dan Busenbarrick 2020-01-01T04:55:17Z

Another possible point of interest. I removed all excess villagers and golems from that chunk and saved the world to the google drive folder linked above. There should be 59 villagers left, give or take a couple. I am curious as to your method for counting villagers for your earlier post. I am certain I didn't get rid of anywhere near 300 villagers.* Could you maybe count those in this world and see if it is registering very many more than 59?

*I stand corrected. See screenshot.