I successfully achieved a migration from XWiki 8. I just wanted to share a few tips, in case someone else is looking to do the same thing. There are some infos on the web, but it’s scattered, and there are some pitfalls to avoid.
Some of those tricks may apply to other (rather old I guess) versions of XWiki
Don’t try to use the integrated export feature
It tends to silently fail, and to generate incomplete XAR archived, without error…
Use Large Export by Space extension
It’s very efficient. It looks unpolished, and you have to check individually every page to export (the child pages are not checked automatically), but it does the job. I exported 1500 pages (XAR archive of 4 GiB)
Adapt your Java container’s max URL size
The Large Export extension generates a long GET request. In my case it was about 70.000 chars. Java containers accept usually a limited size of URL (4 kbytes in the case of Tomcat), so you’ll have to increase that. For Tomcat, that’s the
maxHttpHeaderSize parameter in
server.xml. I set it to 128 kbytes (URL characters are usually among the 128 first of unicode, which are encoded on 1 byte per char).
Increase Java’s max heap space
With my default heap space of 1 GiB, the Large Export extension failed (fortunately with an explicit error, contrary to the integrated export function). Increasing the heap space to 4 GiB did the trick. Don’t forget to set it back to its original value once the export is done, too much heap space is not recommended (the GC could slow things down I believe)
So, that’s about it. Hope it helps