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External Particle Cache Playback Is Broken (2.8)
Confirmed, NormalPublicKNOWN ISSUE

Description

System Information
Operating system: windows 7 sp1
Graphics card: gtx660

Blender Version
version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-09 21:43, hash: 030c7df19da9, type: Release
build date: 09/06/2019, 17:18
platform: Windows

Short description of error

Exact steps for others to reproduce the error
It is simple to recreate, open blender, save the file, assign a psys to the default cube and write it to disk.
Create another cube, add a psys and set it to external cache playback.
Browse to the external cache and Blender can't read the particles it just wrote to disk, or Blender reads only the particles cached on the first frame.

Event Timeline

Philipp Oeser (lichtwerk) lowered the priority of this task from 90 to 50.EditedDec 19 2019, 8:17 PM

Sorry this has been lying around for so long.
Well, old particles are EOL, so I wont be holding my breath here, but I will now go over these particle reports [we have a couple about external caches and many more about other particle issues in 2.8 upwards...] and at least do an initial triage on them...

Can confirm, only reports 4 points found, if I do the same thing in 2.79, all 1000 points are reported found in the cache.
Baked cachefiles seem to be pretty much the same from 2.80 and 2.79 (filesize), with the one exception that 2.79 writes the biggest frame on frame zero test_000000_00.bphys(12kb) whereas in 2.80 this frame is kind of missing, it starts with test_000001_00.bphys(272bytes) -- which is exactly the same as test_000001_00.bphys (272bytes) in 2.79. Not sure this is related though...

@Sybren A. Stüvel (sybren): subscribing you here since you are most familiar with caches?

Philipp Oeser (lichtwerk) reopened this task as Confirmed.Jan 27 2020, 2:27 PM
Philipp Oeser (lichtwerk) triaged this task as Low priority.
Philipp Oeser (lichtwerk) changed the subtype of this task from "Report" to "Known Issue".

OK, will merge the other way around

Same issue. Blender 2.83.7. Mac OS Catalina 10.15.7

Named the Cache > Checked Use Library Path and Disk Cache (Cache step 1 no compression)> Baked the particle physics. Everything looks great. Duplicate the project > open it up > check external in cache settings > navigate to named cache > click accept > only a few particles actually relink.

4 years ... probably time to disable this feature or change description to not confuse users with this disfunction.

There is not a problem to load cache of 2.79 into 3.x ...

Philipp Oeser (lichtwerk) raised the priority of this task from Low to Normal.May 6 2022, 12:06 PM

Not sure tbh why I set this on low prio (probably because particles are EOL, still, there are many other particle bugs/known issues that are normal priority, so will raise prio again).
That being said, changes/fixes are unlikely because of EOL

Thanks for priority ... I can understand to this state point (PS EOL) and I'm not asking to fix that (even it would be great) ... it just seems to me better replace or notify current limit (that is not such hard), than keep it like that for such a long time and let end user to have expectations from feature that is not working.

So how is one supposed to render on a farm without being able to load a particle disk cache? Isn't this an important fix? Perhaps there's another way I'm not familiar with.

You can create a particle system, write a particle disk cache, and send the .blend and cache to the render farm. It should load just fine.

What doesn't work is creating a new particle system and loading a disk cache created by another particle system into that.