Viewer slow first read and what are the shortcuts

[Geremia]

Originally Posted by Geremia

Here's a screencast of how painfully slow ebook-reader loads even for a tiny 9kB EPUB:
This is with Calibre 6.23, recent Nvidia proprietary graphics drivers, Linux

I sped this up by turning on compositing in KDE Plasma (Alt+Shift+F12), but still it could be faster.

[Montana Harper]

This is a problem that I've had for ages, too. My system is absolutely not a potato (see specs below). The first time I open a book with the Calibre viewer after restarting my system (and possibly sometimes after restarting Calibre, but I'm less sure of that) it takes forever. Every subsequent book is fine.

Today I ran the debug when opening a 539KB epub after reboot:

DEBUG: 0.0 GetFileName::__init__.py - loading translations
Initialized urlfixer
QPA platform: windows
devicePixelRatio: 1.25
logicalDpi: 96.0 x 96.0
physicalDpi: 74.88368522072936 x 74.89965870307167
ApplicationPaletteChange event ignored
Using calibre Qt style: True
ApplicationPaletteChange event received
Sandboxing disabled by user.
[0.000] Load of book started
[0.016] preparation started
[0.313] bridge ready
[0.422] iframe ready
[308.203] prepared emitted
[308.234] webview loading requested
[308.391] loading finished

I'm running Calibre 8.2.1 from the same SSD as my OS (Win10Pro, v 22H2), but my libraries are on an internal HDD.

System Specs:
32GB RAM
3.70 GHz AMD Ryzen 9 5900X 12-Core processor
nVidia GeForce RTX 3070 Ti with 8GB onboard memory and up-to-date drivers

I'd actually switched to SumatraPDF because of this, but it doesn't always display epubs properly and doesn't allow me to have persistent highlights, etc., so I'd kind of like to go back of the built-in Calibre viewer, if I can get it to stop taking 5 minutes to load a book every time I reboot my system.

[BetterRed]

I suspect you have something poking it's nose into calibre's cache which is normally at %appdata%\calibre\caches. Try having it elsewhere - e.g. c:\calibre\caches

Set the CALIBRE_CACHE_DIRECTORY Environment variable to get calibre to use it, see ==>> https://manual.calibre-ebook.com/cus...ment-variables

BR

[Montana Harper]

Originally Posted by BetterRed

I suspect you have something poking it's nose into calibre's cache which is normally at %appdata%\calibre\caches. Try having it elsewhere - e.g. c:\calibre\caches

It looks like you were absolutely right. I moved my cache and set the environment variable for it, and both starting Calibre and opening books goes much faster.

[Fleabus]

Like Montana Harper and others, I was plagued with this issue for many years. I've been using calibre since the beginning.. I remember worrying about the install folder becoming calibre2, and wondering if the install folder was going to change with each new version, but I digress.

The take-forever-to-open-a-book problem appeared to be entirely random, completely solution-resistant, irrespective of the size of the book file being opened. Also like Montana, I used an alternate app, FBReader, which opens anything instantly, Just in case I wanted a quick-open for a quick look.

I tried many solutions over the years to no avail, but BetterRed's seems to work. I am cautiously optimistic.

First I tried moving the cache from %appdata% to C:\CalibreCache. That didn't work; same old stuff.

So I moved the cache out of the system partition altogether, to a different partition on the same SSD. D:\CalibreCache has worked like a charm for the past three weeks. Average size ebooks open instantly! Up to 100mb they take ~3-4 seconds.The Shakespeare book, 212 MB, or its ilk, now take ~10 seconds, where they took minutes to open before.

The permissions on a non-system partition are a bit more conventional. That's the only thing I can think of. For this particular gremlin I'm full of theories, but have no answers...

Thanks BetterRed!

[Fleabus]

I can't edit the above post because this is only my second post here, so here's a quick update/progress report.

In April '25 I moved the Calibre Cache out of the system partition to another partition on the same SSD in order to cure the ubiquitous "viewer-slow-to-open-files" problem.

New cache location D:\CalibreCache continues to work a treat.

One thing I want to add:

I have found it necessary to periodically clear the cache in order to keep Calibre, the viewer, and the editor snappy. When these apps begin to slow down, clearing the cache restores quick performance.

I have wiped the cache twice since the last post. So, once a month or so? I suppose that depends on how much use the apps get. Others may find it necessary to wipe the cache more or less often; YMMV...

Hope it helps someone here and there...

[BetterRed]

I empty it every day in my EndOfDay housekeeping process.

I saw the Cache folder had a file named "viewer-reading-rates.json", I have no interest in such data, nor any plugins like Reading Goal that might collect such data.

If I uncheck EPUB in the Preferences->Behaviour->use viewer for: list, and let Windows start the viewer (ebook-viewer is my default program for EPUB) the viewer reading rate data is not collected, The viewer opens just as fast (maybe even faster), and I don't appear to lose any functionality I care about.

BR