In one of my databases, one application query suddenly started to pick Nested-Loop joins instead of Hash-Joins and took almost 6 hours to complete which gets completed in less than 10 secs with Hash-Joins.
The same query in another similar database with same configuration and same data is doing fine and using hash joins. There is no difference in data/stats/OS/init parameter etc. (Though I know that no two databases are same)
About the query:
— It is a simple select statement which selects data from a complex view.
— The view comprises of 5 different tables, four of which have more than 15K rows and one have less then 50 rows.
— Statistics are up-to-date in both databases.
I can see the optimizer behavior using 10053 event for the next run of this query but want to know what else can be checked to know why the plan changed suddenly, in this case, before using 10053 event.
Your valuable inputs on this!!!!