I came across another strange SQL performance issue: Problem was that a SQL statement was running for about 3+ hours in an User Acceptance (UA) database, compared to 1 hour in a development database. I ruled out usual culprits such as statistics, degree of parallelism etc. Reviewing the SQL Monitor output posted below, you can see that the SQL statement has already done 6 Billion buffer gets and steps 21 through 27 were executed 3 Billion times so far.
Statistics and execution plan
Please refer to the execution plan. Due to the functionality of the SQL statement, the execution plan seems acceptable. 3 Billion executions in to the view (at step 21) is also expected, however, why would the SQL statement runs much slower in the UA database ? [ Table names are changed for security reasons. ].