Path: newssvr20.news.prodigy.com!newsmst01.news.prodigy.com!prodigy.com!prodigy.com!in.100proofnews.com!in.100proofnews.com!news2.telebyte.nl!zen.net.uk!btnet-peer1!btnet-feed5!btnet!news.intra.bt.com!not-for-mail From: Rob Cowell Newsgroups: comp.databases.oracle.server Subject: Re: Description of _complex_view_merging Date: Fri, 12 Dec 2003 17:58:09 +0000 (UTC) Organization: not organized Lines: 35 Message-ID: <3FDA01B2.2E59C253@hotmail.com> References: <7c275508.0312120629.7108bdea@posting.google.com> NNTP-Posting-Host: 10.224.110.46 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Trace: visp.bt.co.uk 1071251889 28465 10.224.110.46 (12 Dec 2003 17:58:09 GMT) X-Complaints-To: newsmaster@news.intra.bt.com NNTP-Posting-Date: Fri, 12 Dec 2003 17:58:09 +0000 (UTC) X-Accept-Language: en X-Mailer: Mozilla 4.7 [en-gb]C-CCK-MCD (WinNT; U) Xref: newssvr20.news.prodigy.com comp.databases.oracle.server:249998 Christian Hartmann wrote: > > Hi, > > the Oracle-support told us explicity to set _complex_view_merging to > false to improve the performance of our database after migration from > 8i to 9i. > > Can someone give us a short description what exactly this paramter is > reponsible for? > > Regards, > > Christian I think this is covered in the manuals. A complex statement is something like SELECT FROM tab1 WHERE col1 IN (SELECT col1 FROM tab2) ie, it doesn't have a join clause If _complex_view_merging is TRUE it could be transformed into something like SELECT tabl.col FROM tab1,tab2 WHERE tab1.col1 = tab2.col1 In theory there are more and more powerful join operations available to the optimizer where there is a join clause.