Hmm, that's not what I would have expected. I'm going to ask around and see if there's something I'm missing here, but in the meantime can you try running TUNE TABLE on this table and see if that changes the behavior/query plans at all? https://docs.intersystems.com/iris20253/csp/docbook/DocBook.UI.Page.cls…

Comparing the two, it does look like the slower query is performing a full table scan for some reason, which is very odd. What type of index is row_status_idx? If it is not a bitmap index, could you try adding an additional bitmap index on the field (or changing the type of the index to bitmap)?

Thanks for checking that! Is this the query plan for the slow or fast version of the query, or are the query plans identical between them?