I encountered a curious issue recently, and immediately knew I needed to blog about it. Having already blogged about implicit conversions and how the TOP operator interacts with blocking operators, I found a problem that looked like the combination of the two.
I reviewed a garbage collection process that’s been in place for some time. The procedure populates a temp table with the key values for the table that is central to the GC. We use the temp table to delete from the related tables, then delete from the primary table. However, the query populating our temp table was taking far too long, 84 seconds when I tested it.
Read on to understand why.