Calibre taking 30+ minutes to start with 20K book library

[Luna]

Hello! I'm new here. I can't believe I didn't know about this website and forum!

I posted on Reddit because I had a problem with Calibre and was advised to post it here as well. I have found what causes the problem (and a temporary fix for it) but I don't know WHY it happens. Maybe someone here can help me figure it out?

If there is anything you want to know about my set-up or if you want me to test anything, please let me know!

I will post what I posted on Reddit, because that has all the details:

Start of Reddit post

I'm experiencing extreme startup times with Calibre (8.13.0, now upgraded to 8.14) on macOS 26.1. Opening my library of 20K+ books takes 30+ minutes, often appearing to hang completely before eventually loading.

What works normally:

• Small test libraries (5-10 books) open instantly
• The library itself is healthy, "Check Library" finds no errors
• Database integrity check passes (PRAGMA integrity_check = ok)
• Database size is normal (29MB for 20K books)

What I've tested without success:

• Starting with --ignore-plugins : fast startup
• Disabling all user-installed plugins: still slow
• Disabling device detection and content server: still slow
• Complete network disconnect (WiFi + Ethernet off): still slow
• VACUUM on database: no improvement
• Fresh Calibre install with clean config: still slow
• Different DNS servers (already using 8.8.8.8)

System:

• iMac 2020, 72GB RAM, macOS 26.1 with 20GB library, 63K files, 29MB database
• No custom columns, no saved searches
• Standard metadata plugins only
• Library on internal SSD (not network)

The fact that --ignore-plugins makes it fast suggests a built-in plugin or initialization routine is the culprit, but I can't identify which one.

Has anyone experienced similar issues with large libraries? Any suggestions for further troubleshooting? Thanks in advance!

EDIT (of Reddit post): SOLVED!
Solved meaning I know what's causing the problem and what to do about it, but I still don't know WHY it is happening.

After lots and lots of troubleshooting, I found the following (with a little help from Claude and ChatGPT &#128521:

Calibre took 30+ minutes to start with my 20K+ library, using 46GB RAM (!) and pegging CPU at 100%.

Root Cause: Corrupt/problematic cache folders created during runtime:
~/Library/Caches/calibre/aa/
~/Library/Caches/calibre/ev2/
~/Library/Caches/calibre/gui-thumbnail-cache/
~/Library/Caches/calibre/qwe/

These remain after quit and cause the next startup to hang with Text Services Manager (TSM) failures and massive memory leaks.

TSMSendMessageToUIServer: CFMessagePortSendRequest FAILED(-1)

With 20K+ books = 20K+ failed calls = massive delays + memory leak.

If it happens again:

killall calibre 2>/dev/null
rm -rf ~/Library/Caches/calibre/* /tmp/calibre-* 2>/dev/null
sleep 2
/Applications/calibre.app/Contents/MacOS/calibre

And if the problem persists, reset TSM:

sudo rm -rf /System/Library/Caches/com.apple.IntlDataCache*
sudo rm -rf /var/folders/*/*/*/com.apple.IntlDataCache*
sudo reboot

Startup now takes a few seconds instead of 30+ minutes!

End of Reddit post.

Any help or input is very much appreciated! Thanks in advance!

[kovidgoyal]

caches are supposed to remain after quit, that's the whole point of on disk caches. As usual with macOS, I recommend checking that all the various accessibility tools under the System Preferences->Accesibility are turned off. They typically cause crashes not slowdowns but who knows.

[OokOok]

Interesting. On Windows I started experiencing long startup times starting sometime in the last 90 days. I've got about 5K books, and the FIRST startup takes about 2 minutes, with the "Starting up, please wait...\n\nStarting calibre: loading books..." banner staying onscreen the whole time. If I immediately exit and restart the app when it finally comes up it launches in < 2 seconds. If I go to Task Manager during the long startup I see two threads running: "The main calibre program" and "calibre worker process". If I terminate that latter BEFORE calibre fully loads and then restart calibre, that ALSO results in a quick start.

I don't know how long the "loads quickly after sitting through a long start" behavior lasts. At some point, after being unloaded for an indeterminate period of time, the slow start behavior returns. (For example, if I unload it and go away for several hours before trying to restart then I again have to wait 2+ minutes for restart to complete.)

Currently on 8.14, and this long restart behavior started happening at some point in the 8.x series, but not certain when. Did not exist more than 3 months ago, however, fwiw.

[Luna]

I found something else:

/Applications/calibre.app/Contents/MacOS/calibre (through Terminal):
Fast startup (2-3 seconds)

Open /Applications/calibre.app (through Finder or launching via Spotlight/Alfred):
Slow startup (30+ minutes)

The app bundle launcher clearly behaves differently than the direct executable. Is there an explanation for this?

[Quoth]

About 3 seconds via GUI. 9K ebooks and some PDFs. OS is on SSD and library is on an ordinary SATA HDD.
Linux Mint, old Optiplex 5070 with Intel® Core™ i7-9700 CPU @ 3.00GHz × 8 and 16M RAM. Graphics is poor Mesa Intel® UHD Graphics 630 (CFL GT2). A 4K screen.

[Sirtel]

Mine takes about 10 seconds, over 35 000 books (no PDF files), lots of plugins and custom columns. SSD, 32GB RAM, Intel i7-10875H. Also 4K screen.

The sub-library with about 3500 books takes 6 seconds, so it's probably customizations and plugins, not the number of books.

[theducks]

# of books only applies to the DB (size gets bigger with count and amount of metadata in the GUI) (and maybe some thumbnails) being accessed.
I have way more book entries (a lot are 'empty books' that just doc my paper Library My metadata.db is 60M, but I only have few Notes. I trim the fluff out of comments.

Windows does take some time before the splash screen and it is DEFENDER (taskman), but I have already excluded calibre2, so it is something else (it did get worse starting mid 7.x0)

FWIW My program dirs are on SSD, but my library is on spinning rust.

When was the last time you ran (at least phase1 of) Library Maintenance?

[Sirtel]

My database is 480 MB. Comments are the least of it, I think, as they've all been edited by hand.

Calibre libraries have been excluded from Defender, but not the program itself. I now excluded the program and the startup time is 7 seconds instead of 10. Not perfect, but tolerable.

[Quoth]

Try excluding onedrive and anti-virus.

[Sirtel]

Originally Posted by Quoth

Try excluding onedrive and anti-virus.

The OP is on a Mac, so I guess no OneDrive.

[Luna]

Correct, no Onedrive!

[BetterRed]

Did you try a restart with no plugins?



BR

[Luna]

Originally Posted by BetterRed

Did you try a restart with no plugins?

Attachment 219396

BR

Yes, see my original post. Starts up fast.