Steps to replicate the issue

1. Create 200 to 500 Undefined Pages in a few Confluence Page in within a Space.
2. Navigate to Space Tools > Content Tools
3. Click on Undefined Pages which should list up to 1k of Undefined Pages.

Expected Behaviour
The Undefined Pages list should load immediately and does not cause CPU spike

Actual Behaviour
The Undefined Pages list took sometime to load (~5 seconds) and causes CPU spike (from 7% to 26% in my test) until the Undefined Pages list loaded.

Clicking on the Undefined Pages tab multiple time in a short period (5 times in about 3 seconds) causes the CPU Spike as per the following:

With only one click, there is a small spike (from 7% to 26%) until the undefined pages list loaded.

Notes
With 200K of Undefined Pages:

• Time taken to get the undefined pages from one space took 2m36.777s (0:02:36)
• CPU usage for Confluence process went from ~0% to ~60%, spiked at 150-200% - on 24 cores machine.