Slow loading and saving speed in writer solved by conversion odt -> docx -> odt. Performance trick


Loading and saving time in LibreOffice was five time faster, after re-converting .odt into .docx, then again into .odt.
Few questions to LibreOffice pros, and a performance trick that might be useful to standard users like me.

My mum is writing a book, 605 pages, 230k words, 1.7M chars. No pictures, just few standard tables, normal fonts, only manual references. It was slowly written for >5 years in .odt, started in Debian wheezy, then moved into fresh install of every new Debian. No other hardware or software issues, auto-update, nice 3.2 GHz, multicore x64. Currently Debian Buster 10.6, with libreoffice (1:6.1.5-3+deb10u6).

This year every single time opening of this file lasted ~20 seconds. I’m counting from pressing enter button, to a first appearance of text. Every single pressing toolbar “save button” or Ctrl+S required more than 16 seconds until progress bar reached end. Even automatic LO saving lasted this long.
Not terrible, but annoying when this happens all the time. file loading was almost identically slow after moving to a new SSD, to a fresh install of current Debian. Total file editing time 2118 hours, revision version: 11396, resetting file properties didn’t help.

Very similar timings were on mildly better machine with updated Debian 9, LibreOffice Build ID: 1:5.2.7-1+deb9u11.
I tried changing process priorities in Debian, changing LO settings, cache, others, O/C processors for testing purposes. Tried moving book into few parts, it divided loading time unevenly, first part was processed in 10s, second part was processed 7 seconds.

I though it was about book length and almost bough a new machine. Then I saved this file as a .docx.
Measured time of text showing up was twice faster, only this new MsWord file needed twice as long until it finished loading the rest of the book. But every saving time was only 3 seconds. Then I converted this file again, back into .odt.

Loading lasts 4 seconds now, saving time is 2-3 seconds. File size was 1.0 MB, now is 757 kB.

Both computers, both Debian, both LibreOffice 5 and 6 gave that same result. Afterwards it required only few corrections in Tables of Contents and footnotes, the rest looks identical.

WHY did this happen ? How can hidden formatting slow down reading time that much?

Why did this double-conversion help ? What important information in this file could be lost now?

I’ve notices many others files are loading faster under MsWord. Could we use above re-conversion as general file optimization ? Could LO coders use this in any way?

Is this happening, because file was created years ago, in older LibreOffice 4, moved into 5 and 6 ?
Speed was much faster in OO and LO4 with ~400 pages, but AFAIK this slowing down was spread over time, only mildly worsened in LibreOffice6 . Has anyone else noticed this?


Information loss: I bet your mum uses Writer like a typewriter, i.e. formatting by “hand” using bold, italic, … buttons (or shortcuts), spacing with empty paragraphs, etc. In this case, you lose nothing because no style nor sophisticated encoding is involved.