Undo very slow, even for simple actions like slice and move item

Hi teeramusic. I looked at your project and sure enough, it has a very slow undo. And that's without having any of the plugins or media files available. And with a brand new undo file. When I did a simple split, then did an undo, it took about 6 seconds. Ouch. But I notice that when the undo finally happens, the screen does a strange redraw, like it's struggling. There aren't a lot of tracks, but the project is over 36 minutes. And there seem to be project is over 36 minutes. You seem to have a relatively large number of items, many with take fx. That seems atypical, but I don't know what that all means as far as your problem goes. Not much help, but at least now you know (if you didn't already) that it's happening on a different setup. Reaper 5.20, Win 10/32. Have you tried simplifying the project to narrow it down?

So I tried removing all my 608 instances of item FX and sure enough, things are snappy again. I'm editing audio books and I kind of need them for my workflow. My current workaround is to just drag things out again, but that's not ideal. I've tried to use different save undo state options, but nothing seems to help, including offlining the plugins. It would be great if the devs could have a look at this and make everything snappy regardless of number of plugins!

Confirmed (5.20 x64). Maybe it helps if you disable "Save state as VSTbank" for these plugins (rightclick options in FX browser). Most plugins don't need this. Here only TX16Wx needs it for example. Save the project and test again ...

A workaround for audio books might be to have chapters in sub projects so that your active fx instances are limited to one chapter at a time?

Yeah, subprojects might be the key.

I think I know why it is doing this. The state chunk blobs for the FX you are using are ridiculously massive. Now multiply this by the number of instances. I use a lot of item FX but don't get this problem. But these are more typical FX like EQ, compression, reverb etc. It is specific to the FX you are using. They store crazy amounts of data in the reaper project. Look at these FX datas in the RPP... I think these FX are designed to be used destructively or pre-rendered. They don't seem to be have designed with many running instances in mind. It may be possible for cockos to find a workaround for FX with large state data, but for now, you'll have to move them to subprojects, so they are effectively pre-rendered. You could also 'glue' but that would be destructive. Just to give you an idea what a reasonable FX data chunk is like. This is ReaFir. But this is Izotope Denoiser!

Another thing I noticed: In an old project I can't seem to be able to get rid of the state chunks of at least some of these plugins. Even if I delete all the instances in the project, delete the undo file and empty the undo history, the chunks still show up in the file after I save the project again. Works fine when tested in a new project. Weird.

Why should the undo point for item move have anything to do with item fx state data? Shouldn't reaper simply move the item back to where it was? And if there is something to do with it, why should it affect all 600 instances instead of the FX on the item that got moved? The 600 instances are waves debreath with 5 faders and three buttons. If I enable minimum undo state, shouldn't it only save those 8 parameters?

IMO, I don't think it's REAPER's fault that there is slowness dealing with state on most plug-ins -- plug-ins can store considerable state and still be fast, as long as they generate/parse it quickly. I've seen some plug-ins in the past that have very very complex and heavyweight state loading/saving, often using (particularly slow) public-key encryption as a form of copy protection.

I'd recommend not using plug-ins per item when doing heavy editing. At least, not for all but the most lightweight plug-ins. That project has 600+ instances of Waves Debreath, whose configuration state isn't too high, but still takes a good amount of time to instantiate... Also: if you don't have the plug-in installed, it still takes a while as it tries to load it 600+ times on undo, ugh.