No execution plan is returned only a null value in the DMV sys.dm_exec_query_plan's query_plan column. Any clue as to why? I have used sp_blitzcache 'reads' and 'duration' to show the long running query but no execution plan returns.
Here's a few reasons why queries won't show up in sys.dm_exec_query_plan, the DMV used by sp_BlitzCache:
- The query is encrypted (like an encrypted stored procedure or function)
- The server has Optimize for Ad Hoc turned on, and the query was only executed once
- The server is under memory pressure, and plans are being removed from the cache
- The plan has over 128 levels of nested elements, so sys.dm_exec_query_plan can't show it (but you can still get it via sys.dm_exec_text_query_plan if you want the text version)