Lava / Flowing lava causing huge Java CPU usage

Confirmed on my private server. Basic dual core with 8gb ram and sata drives running ubuntu, jar launched with OpenJdk.

Started looking for the cause in snapshot 42a - appears to still be present in current snapshot. Lava seems to have a worse effect than water 'generally' but both cause significant cpu load increases. Currently developing a new world/map which typically sits at a stable 15% load with a single player and in-game clock driven systems running. Ram use is typically around 3.5Gb with disk i/o being negligible barring the odd data burst. As soon as chunks with FLOWING lava or water are within player range cpu loads start to fluctuate and moving closer to them results in higher and higher loads. Have managed to flatline cpu load at 200% repeatedly on demand.

Specifically with lava, it's flow 'range' also appears to be unpredictable - unable to replicate on demand but on two different 'live' server worlds I've found what appear to be naturally generated lava source blocks flowing down 'steps' with lengths over 50 blocks.

Short drops of either i.e. 2 or 3 block drops with liquid spread onto flat surface does not appear to cause significant impact although inconsistently does see marginal cpu load creep of a few percent. Primary issue appears to be large drops and it's subsequent 'pathing' / 'route finding' on it's way down.

I can confirm and have seen this occurring on my own server

For clarification, is this when lava begins to flow from it's source outwards, or when there is lava that is flowing (showing the animation), but may not actually be moving?

The problem is with lava already flowing, as in the lava drops from the nether ceiling. Nothing actually moving, just the animation running.

Agreed with Ian - lava that's already routed itself i.e. a drop from high level that's already at the floor so, it's displaying a solid block just with animation. From my testing it's also a problem with water on my systems but, it's not always consistent - sometimes it's lava that causes the cpu load and other times it's the water that causes the problem. The only absolute I do have is that when in the overworld, should I load an area with cave systems that have both lava and water I see the cpu load fly up. Removing the source blocks of lava and water in the area see's the cpu loads drop back down to acceptable levels.

Brief update - added a few more systems on the world I'm building at the moment and saw my cpu load creeping up again. Having run around under my spawn area and filled in around a dozen large (drop and route) water and lava falls I've clawed about 10% back though. This is probably going un-noticed in single player and lightly loaded servers but any server with 10+ players running around different regions is basically facing a game killer.

I would hope this would have been addressed in the latest snapshot, the issues added in 1.8 have been fixed to add in issues with CPU ... god help any very large run servers with 10+ users

To reiterate, this bug was first identified in version 42a and is still present through versions to current one 45a. It's also demonstrated on multiple server o/s platforms with multiple java configurations. Modifying launch parameters makes little to no difference and neither does varying between launching from cli or via a management application such as mcma or mineos.

I appreciate that people are busy and have plenty of things to work on but can we please have an update or at least an acknowledgement that this bug is being looked or has been flagged for further attention? At this point, it literally is a server killer if player base exceeds much more than 10-15 users and as such renders further development of planned projects or developments on the platform essentially pointless!

Once again sad to say this is yet another re-occuring issue in 15w46a i would've liked to have seen squashed

bug STILL present in 46a update - single player on server, stood stationary next to a waterfall also with a lava fall nearby, cpu load at 40%.

come on guys, this is getting stupid now.

Also affects Windows 10

Once again such a serious bug is grossly overlooked, very much still present in latest snapshot 15w47a

Still present in 47b

Naturally still present in 47c

Still exists in 15w49a

still here in 49b

Still in 50a

This is such a very big killer for servers and still, nothing has been done about it, im a little disappointered in what appears to be fixes for easy things getting done and the bigger ones left by the wayside

Still present in 16w02a

Still present in 16w06a. I think this should really be fixed before any pre-release version is published.

This may or may not actually be linked in with https://bugs.mojang.com/browse/MC-94438 will know next snapshot i guess for sure

Is this still an issue in 16w15a?

yes

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