Switch off “_rowsets_enabled” in Oracle Database 12c

Please find a recent update here:

and more important:

Twitter is a good thing. I get alerted on things I haven’t seen before. And sometimes some things are more than interesting.

This one is actually proven by Jonathan Lewis – and you can read all the details in Jonathan’s blog post here:

• https://jonathanlewis.wordpress.com/2015/11/09/wrong-results/ 

There seems to be a realistic chance to get wrong query results displayed (regardless of using SQL*Plus or a JDBC or any other client – see the comment by Stefan Koehler below Jonathan’s posting) because of the row sets feature in Oracle 12.1 allowing faster initial processing of query results.

You’ll find this in the query information (marked in bold red):

Column Projection Information (identified by operation id):
-----------------------------------------------------------
   1 - "K"."KONTO_ID"[NUMBER,22]
   2 - "KWP"."WAEHRUNG"[VARCHAR2,20], "SV"."SONDERVERMOEGEN_ID"[NUMBER,22],
       "K"."KONTO_ID"[NUMBER,22]
   3 - "KP"."KONTO_FK"[NUMBER,22], "KWP"."WAEHRUNG"[VARCHAR2,20],
       "SV"."SONDERVERMOEGEN_ID"[NUMBER,22]
   4 - (#keys=1) "KP"."KONTO_FK"[NUMBER,22],
       "KP"."SONDERVERMOEGEN_FK"[NUMBER,22], "KWP"."WAEHRUNG"[VARCHAR2,20]
   5 - (rowset=256) "KP"."KONTOPOSITION_ID"[NUMBER,22],
       "KP"."SONDERVERMOEGEN_FK"[NUMBER,22], "KP"."KONTO_FK"[NUMBER,22]
   6 - (rowset=256) "KWP"."KONTOPOSITION_FK"[NUMBER,22],
       "KWP"."WAEHRUNG"[VARCHAR2,20]
   7 - "SV"."SONDERVERMOEGEN_ID"[NUMBER,22]
   8 - "K"."KONTO_ID"[NUMBER,22] 

Roy did some analysis yesterday as well (and now our Optimizer Support Experts look into this case to check whether any other wrong query result bugs are related to this topic). Because there are some open WRONG RESULTS bugs in this area, some of which were filed within the past week, we’d recommend to switch this feature off at the moment.  For instance these bugs are related to this misbehavior:

• Bug 20960570: LEFT OUTER JOIN RETURNS INCORRECT RESULT
• Bug 22173980: WRONG RESULTS WHEN “_ROWSETS_ENABLED” = TRUE

Recommendation – Updated (Nov 15, 2015)

Please read the update blog post here: