_rowsets_enabled – Apply patch and use the default

I while back I blogged about issues with “rowsets“, a new Oracle 12c feature which unfortunately had two known wrong result (WQR) bugs: Switch off “_rowsets_enabled” in Oracle Database 12c UPDATE: _rowsets_enabled in Oracle Database 12c What does “rowsets” actually mean? I’d like to thank Sankar, our Development manager for providing this explanation which sheds some light on how important this feature actually is: “Rowsets is a SQL execution performance enhancement introduced in Oracle RDBMS release 12.1 and further extended in a future release of the Oracle Database. Prior to 12.1, data processing in the SQL layer were done on…

UPDATE: _rowsets_enabled in Oracle Database 12c

Please find a recent update here: _rowsets_enabled – Apply patch and use the default Last week I did post this entry with a strong recommendation to disable _rowsets_enabled in Oracle Database 12.1.0.2: Nov 10, 2015: Switch off _rowsets_enabled in Oracle Database 12c Today I can give you an update, more insight information and better workarounds. Credits go to our DWH and Optimizer people (thanks to Hermann, Angela, Nigel and Mohammed). When is the problem happening? When a hash join operation receives rowsets from its right input but then produces one row at a time as output. This explains why one…

Switch off “_rowsets_enabled” in Oracle Database 12c

Please find a recent update here: UPDATE: _rowsets_enabled in Oracle Database 12c and more important: _rowsets_enabled – Apply patch and use the default 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…