I have a server in the US which acts as the master, and slaves in Asia and Europe. Everything works as expected, except if a user on either slave adds a category to a file, that file never appears in the category page.
Steps to get the image to appear on the category from the slave server: 1) Perform a null edit on the file page. 2) Purge the cache of the category page. Occasionally the file will appear without having to do the null edit, sometimes several null edits are necessary for the file to appear.
If the category doesn't exist the images appear on the first page load of the new category. The wiki in question has about 10,000 files with extensive categorization. I'm not able to reproduce the problem on any other wikis which also exists on the slave servers and share configuration files. But those wiki's don't have very many files on them. How can I go about troubleshooting this?