ePub conversion capacity limits?

[HarryT]

I seem to be approaching some sort of "limit" in doing Mobi to ePub conversions in Calibre. A "normal" size novel converts in a few seconds, but large books seem to take exponentially longer and longer. I've recently created a number of large "omnibus" editions of books:

A Mobi book with 8MB of HTML source took 9 minutes to convert.
A Mobi book with 10MB of HTML source took 20 minutes to convert.

This is on a fast, modern, PC with a dual-core CPU and 4GB RAM.

Given that both the books have well-formed HTML, and short chapters, is there any reason for this seemingly exponential rise in conversion time? I would have expected that a 10MB book would take 10x as long to convert as a 1MB book, but it's way, way, longer than that.

Is there any absolute upper limit to the largest book that Calibre can convert?

[ChristopherTD]

FWIW I encountered the same thing when I recently did a bulk convert of a whole bunch of LIT files to ePub. Buried in the middle of them was the Encarta Pocket Dictionary and I had to cancel that after it had been running for 20 minutes or so. All the others were very quick. Perhaps it is related to number of chapters, or references?

[kovidgoyal]

the bottleneck in conversion is CSS parsing. MOBI input files can sometimes generate a lot of CSS that has to later be parsed. Unfortunately, the only ready to use CSS parsing library I could find uses regexps to parse CSS and is really slow, it's time goes up exponentially with the size of the CSS.

[HarryT]

Thanks for explaining that, Kovid. It's not a problem - I've not yet created a Mobi book that's so large that it won't convert - but it's nice to understand the reason for it.