Panel Wizard Slowness
Explanation
The Panel Wizard can take a long time to open, or time out, on a large wiki.
Cause
The "Panel List" tab does not merely name the available Panels, it renders each of them so you can see what you are dragging. Every Panel that queries the wiki, such as Recently Modified or Navigation, therefore runs its query while the section loads, and a wiki with many pages or many Panels pays for all of them at once. The behaviour is tracked as XWIKI-16579.
Solution
Set the layout without opening the section, by editing the XWiki.XWikiPreferences xobject of the XWiki.XWikiPreferences page directly and filling in the six properties the Wizard would have written: "Panels displayed on the left", "Panels displayed on the right", "Display the left panel column", "Display the right panel column", "Width of the left panel column" and "Width of the right panel column". The two list properties take a comma-separated list of Panel page references, so the Wizard is only a convenience over them. Panels Bundled with XWiki gives the references to use.
FAQ
Is the Panels home page slow for the same reason?
No. It lists the Panels in a table without rendering them, so it stays fast however many there are.
Would asynchronous rendering fix it?
It helps the pages a Panel is displayed on, not the Wizard, which needs the rendered output before it can show it to you.
