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11gR2

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Oracle 11gR2 and 12cR1 on Oracle Linux 7

I did a quick update of my Oracle installation articles on Oracle Linux 7. The last time I ran through them was with the beta version OL7 and before the release of 12.1.0.2.

The installation process of 11.2.0.4 on the production release of Oracle Linux 7 hasn’t changed since the beta. The installation of 12.1.0.2 on Oracle Linux 7 is a lot neater than the 12.1.0.1 installation. It’s totally problem free for a basic installation.

You can see the articles here.

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Don't delete your flashback logs manually

What happen when someone will delete Oracle flashback logs ? You probably don't notice it until you will try to flashback database or bounce instance. 
There is no hope for flashback database without flashback files but there is still way to start your database again without recovery or data loss.

Here is a scenario:
[oracle@dev-6 alert]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Tue Jul 1 09:34:18 2014

Copyright (c) 1982, 2013, Oracle. All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

New Version Of XPLAN_ASH Utility

A new version 4.1 of the XPLAN_ASH utility is available for download.

As usual the latest version can be downloaded here.

This version in particular supports now the new 12c "Adaptive" plan feature - previous versions don't cope very well with those if you don't add the "ADAPTIVE" formatting option manually.

Here are the notes from the change log:

- GV$SQL_MONITOR and GV$SQL_PLAN_MONITOR can now be customized in the
settings as table names in case you want to use your own custom monitoring repository that copies data from GV$SQL_MONITOR and GV$SQL_PLAN_MONITOR in order to keep/persist monitoring data. The tables need to have at least those columns that are used by XPLAN_ASH from the original views

Oracle 11gR2 and 12cR1 on Oracle Linux 7 beta

I’ve been having a play with Oracle Linux 7 beta over the weekend. Not surprisingly my first thoughts were to install the Oracle database on it.

As expected, the installations were almost identical or Fedora 19.

Analysing Parallel Execution Skew - Without Diagnostics / Tuning Pack License

This is the third part of the video tutorial "Analysing Parallel Execution Skew". In this part I show how to analyse a parallel SQL execution regarding Parallel Execution Skew.

If you don't have a Diagnostics / Tuning Pack license the options you have for doing that are quite limited, and the approach, as demonstrated in the tutorial, has several limitations and shortcomings.

Here is the video:

Analysing Parallel Execution Skew - Data Flow Operations (DFOs) And DFO Trees

This is the second part of the video tutorial "Analysing Parallel Execution Skew". In this part I introduce the concept of "Data Flow Operations (DFOs)" and "DFO Trees", which is what a Parallel Execution plan is made of. DFOs / DFO Trees are specific to Parallel Execution and don't have any counterpart in a serial execution plan.

Understanding the implications of DFOs / DFO Trees is important as prerequisite for understanding some of the effects shown in the later parts of the video tutorial, hence I covered this as a separate topic.

Note that this tutorial also demonstrates some new 12c features regarding Parallel Execution, in particular how Oracle 12c now lifts many of the previous limitations that lead to the generation of multiple DFO Trees.

Here is the video:

New Version Of XPLAN_ASH Utility

A minor update 4.01 to the XPLAN_ASH utility is available for download.

As usual the latest version can be downloaded here.

These are the notes from the change log:

- More info for RAC Cross Instance Parallel Execution: Many sections now show a GLOBAL aggregate info in addition to instance-specific data

- The Parallel Execution Server Set detection and ASSUMED_DEGREE info now makes use of the undocumented PX_STEP_ID and PX_STEPS_ARG info (bit mask part of the PX_FLAGS column) on 11.2.0.2+

- Since version 4.0 added from 11.2.0.2 on the PX *MAX* DOP in the "SQL statement execution ASH Summary" based on the new PX_FLAGS column of ASH it makes sense to add a PX *MIN* DOP in the summary to see at one glance if different DOPs were used or not

Extension Bypassed Because of Missing Histogram

Today, while tuning a fairly complex query experiencing wrong cardinality estimates, I noticed something I was not aware of. Hence, I thought to write this short post to illustrate how to reproduce the problem I experienced…

New Version Of XPLAN_ASH Utility

A new version of the XPLAN_ASH tool (detailed analysis of a single SQL statement execution) is available for download. The previous post includes links to video tutorials explaining what the tool is about.

As usual the latest version can be downloaded here.

The new version comes with numerous improvements and new features. The most important ones are:

  • Real-Time SQL Monitoring info included
  • Complete coverage including recursive SQL
  • Improved performance
  • 12c compatible
  • Simplified usage