Sort Exceeded Memory Limit

I am having a recurring issue that I seem to be able to patch, but I would like a more permanent solution. My client has hundreds of items they need to have on their website at a time, for ecommerce consignment sales. I think currently there are over 900 items in the CMS, which can cause significant problems, one of which is this:

Database Issue: Multiplanner encountered a failure while selecting the best plan :: Caused By :: Sort Exceeded memory limit of 104857600

Basically I need a way for my client to continue to have as many items as they do on their website, without causing this error. My current fix of just deleting as many sold items as possible seems to temporarily fix the issue, but it does not solve it permanently.

Here is my public share link:

Where are you seeing the error, and when is the error occurring?