MacOS Catalina 10.15.7, GPU GeForce GTX780M 4GB, Samsung SSD 860 EVO, CPU Intel i5 3.1 GHz, memory 16 GB

What I found on Illustrator v26.4.1, v27.6.1:
1) Grids in Back (on) + Show Grid + View using GPU + User Interface Canvas Color: White >> performance degradation
2) Option Grids in Back (off) + Show Grid + View using GPU + User Interface Canvas Color: White >> performance good
3) Option Grids in Back (on) + Hide Grid + View using GPU + User Interface Canvas Color: White >> performance good
4) Option Grid in Back (on) + Show Grid + View using CPU + User Interface Canvas
Color: White >> performance good
5) Option Grids in Back (on) + Show Grid + View using GPU + User Interface Canvas Color: Match Brightness >> performance good

That is, the main performance hit on my spec is on the GPU when Grids in Back and Canvas Color: White are enabled.

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An even stranger observation is when a grid of lines in the background reduces performance. Setup: Grid in background (on) + Show grid + View using GPU + User interface canvas color: White.

1) I open Preferences and change the grid style to dots.
2) I close Preferences. A grid of dots is rendered on the screen.
3) I open Preferences and change the grid style back to lines.
4) I close Preferences. The grid of lines renders on the screen... And now performance is normal! While the document is open.

Restarted Illustrator. The trick of changing grid styles doesn't work anymore. Performance remains poor.

We’re getting close to 1.5 years since this incredibly serious bug was introduced, and there’s no sign it will be fixed soon. I can’t stress this enough: I can not use Illustrator the way I want to while this bug exists. With Grids in Back turned on, Illustrator is unacceptably slow and almost impossible to use.

PLEASE FIX THIS BUG.

@kitgrose Yep, it seems improved for me, but nowhere near fixed or like 25.2.3. Toggling grids in back on and off yields pretty different performance. I think we’re probably seeing the same thing, just describing it slightly differently?

Contrary to Marc's comment, Illustrator v27.0 *does* seem to substantially improve the issue for me, at least doing the same trivial test I described below (nudging a rectangle around a 24px square artboard in Outline view or with Grids in Back turned on). It's now performant enough that I can use Outline view again.

I do notice that panning the artboard and other similar operations is still noticeably laggier with Grids in Back enabled. Performance for these kinds of operations is still nowhere close to the last unaffected release (v25.2.3), but I'm not seeing any more multi-second delays and beachballs in this release (at least in my early testing).

I’m still seeing this issue with Illustrator 27.0.0. Maybe performance is slightly better, but there’s still a huge difference between grids in front and grids in back.

I’m still seeing this issue in Illustrator 26.5.0.

Illustrator v26.3.1
Windows 10 Pro 21H2
AMD 3900X
32 GB RAM
Nvidia 3080

1. Does it work fine with grid as dots in Preview / Outline mode?
NO

2. Does it differ from grid as lines in these modes?
NO

3. What is slow for you exactly? How severe?
Extremely slow and laggy. Grids are UNUSUABLE in Preview and Outline views

4. Is there a difference if you disable 'Grids In Back' option?
YES (but I don't want grids in front when working)

5. What are you lines/subdivisions settings?
Lines, Gridline every 4px, 8 subdivisions

This problem with grids has been here since v25.3 (I can confirm with Kit Grose findings) and still hasn't been fixed. It's been OVER A YEAR and I have been unable to use GRIDS at all.

The problem remains...

ai v26.4.1
MacMini (M1, 2020)
Chip Apple M1
RAM 16 GB
macOS 12.4

1. Does it work fine with grid as dots in Preivew / Outline mode?
No

2. Does it differ from grid as lines in these modes?
NO

3. What is slow for you exactly? How severe?
It's a nightmare

4. Is there a difference if you disable 'Grids In Back' option?
YES

5. What are you lines/subdivisions settings?
Dots, gridline every 24pt, 3 subdivisions

The original post here is 1 year 3 weeks 4 days old. Adobe, you are losing so much credibility over this bug.

Will this be fixed by the anniversary of the original post? We’re about 3.5 weeks away from that. Adobe, do you have an update for us?

testing this out, disabling 'grids in back' makes grid work as expected both lines and dots. turning 'grids in back' on, completely breaks performance. also, i noticed that even after disabling 'grids in back' rendering now occurs via cpu, and gpu is not available without restarting illustrator.

ai v26.3.1
iMac (Retina 5K, 27-inch, 2019)
3.6 GHz 8-Core Intel Core i9
Radeon Pro 580X 8 GB
macOS 12.3.1

OK, I've now tried 9 separate releases and the issue definitely arrived in the v25.3 update (it does not affect v25.2.3 or earlier releases in my testing).

From v25.3 onwards, it's very clear when grid in back is enabled, because just switching to outline mode (or switching the grid style to dots) takes ~7 seconds (it's instantaneous when grids in back is disabled).

1. In preview mode, it runs substantially worse with grid as dots while the grid is in back
2. I'm not aware of how to make outline mode use grid as lines for comparison, but the app runs *much* slower when the grid is shown as dots.
3. As Marc noted, the whole app runs meaningfully slower when grid is in back. For my tests I'm deliberately focused on only the simplest tasks. I have a single 24px × 24px artboard with snap to grid turned on, and I draw a rectangle on it. It runs slower with grid in back in preview mode, but fast enough to be usable. It runs extraordinarily slow in outline mode, though. Some example operations that run slow: nudging the rectangle with the arrow keys, space-bar panning.
4. Yes, with the grid in front, the performance improves dramatically
5. I have grid lines set to 8px with 8 subdivisions

Attached is a trace captured in Apple Instruments. Run 1 shows preview mode with grids in front. Run 2 shows preview mode with grids in back. Run 3 shows outline mode with grids in front. Run 4 shows outline mode with grids in back. In all four runs, I attempted to hold spacebar and drag pan the artboard in circles around my screen.

My Mac is a 2018 3.2 GHz i7 Intel Mac mini with 32 GB RAM, and I'm running Illustrator with UI Scaling set to its smallest setting on an old-school Apple Thunderbolt Display at its native 2560 × 1440 resolution.

My grid settings haven't changed for a long time, so this issue is unlikely to have been introduced much before the issue was reported.

Here’s my results for panning, zooming and object dragging tests with an almost empty document (a few rectangles) and Illustrator 26.3.1 on an Intel 2019 Mac Pro.

### Preview mode:

Grids off = 60fps.
Grids on, lines, grids in front = 60fps.
Grids on, lines, grids in back = ~2fps with frequent 4+ second freezes.

That’s with gridline every 512, and 512 subdivisions. I would have tested it with the dot grid style, but switching from lines to dots crashes Illustrator every single time.

### Outline mode:

Grids off = 60fps.
Grids on, lines, grids in front = 60fps.
Grids on, lines, grids in back = Illustrator crashed.

What’s slow? Everything. The entire app. Even navigating menus in the menu bar is slow and laggy, with frequent long freezes. This is horribly broken, and we’re closing in on a full year for the issue.

Windows 10, 26.3.1, Intel Core i7-4770, 3.4Ghz, 24GB RAM, Nvidia GeForce GTX 770

1. No, having grids as dots makes it even slower, in both modes, EXTREMELY slow. Dots are almost invisible, and no subdivisions dots are rendered it all it seems. When dots are in front, they work fine, although are still almost invisible.

2. Grid behave a bit better in Outline than it was in the previous version, but not as good as it was before.

3. I literally can’t move, pan or zoom with dots. Preview mode works fine with lines.

4. Ghosting, when a moved object is still displayed in its previous position, seems to be longer with grids in front.

5. 10/10mm

Grid performance is not fixed

Grids is still broken after a year. This issue also occurs on Windows 10. Both OS and drivers are up to date.

I have tried the beta and the most recent update of Illustrator 26.3.1 and grids performance is terrible. It hasn't been working properly ever since version 25. I initially thought is was my computer. Where even basic templates with grids enabled tanked performance to make it unusable. After changing system to a Ryzen 9 with an RTX 3080 the performance with Grids in GPU preview (and pretty much any view when grids in back is enabled) the poor performance is still happening.

I have tried Illustrator on 2 systems Intel i7 with GTX 1070 and Ryzen 9 with RTX3080 and the poor performance of grids still occurs.

This really needs to be addressed as using grids is a basic feature (of any design software) and currently in Illustrator is doesn't work and hasn't worked for a long time now.

I’ll do more testing, but so far I’m not seeing any difference with Illustrator 26.3.1.

I have now tested v26.3.1 as noted, and while it has apparently made a significant improvement for me, Outline View still runs much more slowly when grids in back is enabled.

I've posted a short recording demonstrating the difference in performing a series of nudges when grids in back is switched off and then when it is switched on here: https://twitter.com/kitgrose/status/1526809781121732608

I can also confirm this issue still persists for me in the Illustrator 26.3.0 release. In fact if anything the issue has gotten worse for me.

I've separately installed the 26.4.0 beta build and the issue is not resolved in that release either. On a 24 pixel square document with a 1px grid showing, attempting to open Outline View doesn't do anything but trigger the beachball cursor on my 2018 i7 Mac mini for at least a couple of *minutes*.

Unfortunately, this is not resolved for me with Illustrator 26.3.0 release version.