Garbage collection can affect performance in some cases, especially with very high cache sizes. Garbage Collection is a CPU and Disk intensive activity that, by default, involves iterating through the entire cache structure and deleting enough files to bring down the cache size as per the limits imposed by the caching configuration.
Garbage Collection is Automatic by default, which means that the Proxy server has a dedicated "Garbage Collection Thread" which periodically wakes up to inspect the cache and perform Garbage Collection if needed.
Using the admin GUI, Garbage Collection can be changed to Scheduled which disables the in-process Garbage Collection thread. This can help improve performance, as Scheduled Garbage Collection is achieved using the cachegc command line utility and can be configured to run only at specific times on specific days.