RE: 12c Optimizer and mis-calculations.
From: Iggy Fernandez <iggy_fernandez_at_hotmail.com>
Date: Wed, 11 May 2016 09:55:04 -0700
Message-ID: <BLU179-W62D0435144B0B2F7D7F77BEB720_at_phx.gbl>
re: with or without adaptive optimization in effect Even if adaptive optimization is turned off, there may still be "extended column statistics" that were created when adaptive optimization is in effect. You may want to get rid of them. A script is at http://www.toadworld.com/platforms/oracle/w/wiki/11586.completely-disabling-adaptive-query-optimization-in-oracle-database-12c.
Date: Wed, 11 May 2016 09:55:04 -0700
Message-ID: <BLU179-W62D0435144B0B2F7D7F77BEB720_at_phx.gbl>
re: with or without adaptive optimization in effect Even if adaptive optimization is turned off, there may still be "extended column statistics" that were created when adaptive optimization is in effect. You may want to get rid of them. A script is at http://www.toadworld.com/platforms/oracle/w/wiki/11586.completely-disabling-adaptive-query-optimization-in-oracle-database-12c.
From: dimensional.dba_at_comcast.net
To: oracle-l_at_freelists.org
Subject: 12c Optimizer and mis-calculations.
Date: Wed, 11 May 2016 09:11:56 -0700
Had to share: At one of my clients I was called in the middle of the night to look at a slow running query (9+ hours) on 12.1.0.2.0 on a X5 Exadata on a EDW. When I pulled the execution plan from the cursor cache the calculated numbers were little off (look at rows/bytes/Cost) by about 9 orders of magnitude as the query actually only generates 2.9 million rows in about 6 minutes. -------------------------------------------------------------------------------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |-------------------------------------------------------------------------------------------------------------------------------------------------------------------| 0 | INSERT STATEMENT | | | | | 29P(100)| | | | || 1 | PX COORDINATOR | | | | | | | | | || 2 | PX SEND QC (RANDOM) | :TQ20001 | 2556T| 15E| | 3089M (5)| 20:26:25 | Q2,01 | P->S | QC (RAND) | This bad optimizer planning with estimated statistics or even 100% statistics has been troublesome of late on 12c especially for out of the box applications.The variations in calculation of overall size normally appears in tempspc usage with and without adaptive planning in effect.The extreme miscalculated values normally translate to queries that you kill otherwise they run for days before they die some unnatural death on their own. The fix is normally just to reverse the table order of the joins the optimizer chose for the Fact versus the Dimension tables and then the query runs in minutes instead of days. Matthew ParkerChief TechnologistDimensional DBA425-891-7934 (cell)D&B 047931344CAGE 7J5S7Dimensional.dba_at_comcast.netView Matthew Parker's profile on LinkedInwww.dimensionaldba.com
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