Whenever (long-lived) rising particles are confined by a block above (or inside) and an extended piston head to the West, the game's framerate drops sharply, easily to single-digit levels.
I originally encountered this when crushing large quantities of Blazes using sticky pistons and blocks, but I can also reproduce the lag using a row of campfires and extended normal pistons.
Steps to reproduce:
1. Build a row of pistons, at least 12 long, all of which will extend to the East. Place a line of redstone to extend them all at once, but leave them retracted for now.
2. 2 blocks east and 2 blocks down from the pistons, place a row of campfires with hay bales beneath them (so the smoke lasts longer)
3. 2 blocks east and 1 block up from the pistons, place a row of blocks which will block the smoke particles (e.g. stone or glass)
4. Extend the pistons and watch the framerate quickly drop to single digits.
5. Retract the pistons and watch the framerate instantly return to its previous level.
If the setup is rotated to face in any other direction, the lag is much less severe but is still noticeable in the Alt+F3 framerate graph.
This is quite bad with campfires, because the lag will be felt by any players within about 200 blocks regardless of the direction they are facing, and setting Particles to "Minimum" has no effect (unlike with Blazes, whose smoke will promptly disappear), making this a significant risk for griefing on servers.
Possibly related to MC-124170, though that one was marked as Resolved in 1.14.2 while this one still happens in 1.14.4 (as well as in earlier 1.14 releases).
Does not occur in version 1.13.2 or earlier.
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violine1101
Can confirm. I attached a screenshot showcasing the setup used to reproduce this issue.
It looks like this was fixed in Snapshot 19w44a ("Vertically moving particles now perform better when colliding with blocks.") - the above described campfire scenario no longer causes any noticeable lag.
Blaze smoke still causes noticeable lag as of 1.15 Pre-release 1 (framerate drops from 160 fps to 90 fps, though VSync causes it to drop all the way to 40 fps due to the irregular nature of the lag, having many fast frames followed by one slow one), but it's nowhere near as bad as it was in 1.14.4 (240 fps down to 2 fps).
FACS01
still on minecraft 1.15 pre-release 1, using /particle minecraft:smoke to test it
My previous test was done in Creative mode, but I just tried my blaze farm in 1.15.2 and it's just as laggy as before.
This bug still present in 20w27a, reporter?
As noted above, campfire smoke no longer causes lag, but Blaze smoke still does.
See the two new screenshots - there are 24 Blazes inside a small glass box, and when I activate the piston which extends to the East, the framerate drops significantly. The other 3 pistons don't have this effect.
As of 1.16.2, this scenario no longer appears to cause lag - there is a very brief drop in framerate while the east-facing piston is in the process of extending, but it goes back to normal afterwards (and does not lag when retracting, nor do any of the other pistons result in any lag at all)
ampolive
Can confirm in 1.17.1. There is basically no lag with campfires, but there still is a noticeable lag spike with blaze smoke. Nowhere as severe as the previous versions though, judging by the screenshots.
[Mod] Jingy
Cannot reproduce in 1.20.3 Pre-Release 3. When replicating the setup shown in the original images of the issue, the game does not suffer from frame loss.
1.14.4:
[media]
1.20.3 Pre-Release 3:
[media]
Fantastime
Is this reproducible in the latest version of the game?