Best way to merge two databases with large overlaps?

I may not actually need to do a full merge. Just a quick comparison of entries (would love to export author, year, title in flat files), import to a conventional database and then run a join.

I had found that entries from one author present in previous libraries (Zotero and Mendeley) were not found when I searched in JabRef (“No entries present”). This seems to be an intermittent issue that occurs when I have hundreds of megabytes of swap memory under Ubuntu. I’ve also seen it under Windows.

My browser keeps chewing up more and more memory over time. If I don’t keep it open I don’t have this problem in JabRef

I have 8GB physical memory and a similar amount of swap under Ubuntu, so it isn’t a hardware issue