Our SP2010 farm have been used for 5 years. In recent few months, we find all the workflow shows up red warning message "Due to heavy load, the latest workflow operation has been queued. It will attempt to resume at a later time." regardless which workflow and when it is run. We tested in mid-night for a simple workflow the message also show.
Also we found all workflows are running slow compare to 1 year before. We have retention policy setup for workflow history (delete after 3 months). Is there anything we can do?