I upgraded to Fedora 26 the day of the official public release earlier this week and, long story short, ended up screwing up my installation, so I did a partial reformatting . My disk layout is the following:

`/dev/sdb` is the SSD where root is mounted and `/dev/sda` is a normal HDD where I have my `/home` partition. I decided to do a clean install of Fedora 26 instead of trying to repair my botched upgrade via `dnf`, so I reformatted all partitions in `/dev/sdb`, the SSD and re-installed Fedora 26, keeping the `/home` partition intact. The installation went fine and everything seems to be working normally again except for one thing: Zhs autocompletion is now dog slow with larger directories.

Zsh is my default shell and I have a plethora of plugins installed (Oh My Zsh, FZF, etc.) so I figured one of these might've gone out of whack during/after the upgrade so I switched to Bash: same thing, autocomplete takes a good 10-30 seconds (depending on dir size) to come up. I installed some more shells to troubleshoot the cause and, to my surprise, `tcsh` and `fish` work absolutely fine. Under the same setting, these two perform perfectly fine where Bash and Zsh would hang for a good +10 seconds.

I've done the usual diagnostics with Bash, whose config is pretty vanilla compared to my Zsh install: `strace`, `set -x`, etc., but couldn't find much of interest. Also ruled out FZF as the problem as the slowness persisted after uninstalling it... Still my gut tells me this must be some sort of weird hashing/caching problem of the completion engine that somehow affects both Zsh and Bash, but I don't really have any evidence to support that. Autocompletion with smaller folders (few files, few subdirectories) works fine across all shells I've tried. Other things I've tried is to run `fsck -A -y` to make sure I don't have any corrupt partitions and also re-installed `bash-completion` and `zsh` just in case some metadata or cache had corrupted.

I think what's really intriguing here is the fact that `tcsh` and `fish` have 0 problem autocompleting anything I throw at them, but Bash and Zsh don't. Does anybody know what's going on here? Big thanks to whomever sheds some light into the matter!

I do not think bash and zsh uses the same cache for this.
You can try to create a new user and test if that works as expected.
I would try to reset those caches, probably they remember a non-existent directory (or more).

Just for grin's maybe install clean fedora 26 to a flash drive and see what it does.

So many things going on I can guess. I've never trusted upgrades.

Guess you could run top or other performance tests to see if you can find issue. Look at logs?

1 members found this post helpful.

For bash, you (royal plural, not you in particular) have to set up completion.
In my F25, /etc/profile.d/bash_completion.sh checks for the existence of .config/bash_completion and sources that if so; else it sources /usr/share/bash-completion/bash_completion. Might be worth deleting the .config version if it exists.
Never used zsh that I can remember, so can't offer an opinion there.

FWIW I usually let new releases of Fedora "settle" for 4-6 weeks so all the kinks can be ironed out. Maybe this is one such.

Problem solved! I was toying around with `perf trace` following jefro's advice and as lines and lines of output scrolled past I caught a glimpse of a few weird calls to libnotify from Konsole, my default terminal. That seemed weird since after the reformat I no longer had any desktop notification daemon installed (I use i3, which doesn't come with one, you see). That gave me the idea to try a different terminal emulator. So I tried `urxvt` and lo and behold, the issue disappeared. I also tried with `gnome-terminal` and no probs at all! Could it be then that Konsole was trying to fire off a desktop notification via dbus/systemd but timing out because there was no libnotify daemon installed to respond to the request? So I installed `dunst`, which is the daemon I was using before the upgrade and, as I suspected, autocomplete slowness in Konsole is gone!

So I have no idea what the heck Konsole tries to do when autocomplete is invoked because I never see any notifications pop up, not even after installing the daemon, but, at any rate, the issue seems to be fixed now.

I think I'll be taking this one to the KDE team and see what their thoughts are because, even though it was kind of my fault for not having a notification daemon installed, the other terminals I tried handled the problem just fine.

Anyway, thank you all for your help!