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Clemens Bleile

DOAG 2017: avg_row_len with virtual columns

By | Database Administration & Monitoring, Database management, Oracle | No Comments

At the DOAG I attended a session “Top-level DB design for Big Data in ATLAS Experiment at CERN” provided by Gancho Dimitrov. The presentation was actually very interesting. As part of Gancho’s improvement activities to reduce space in a table he stored data in a 16 Bytes raw format (instead of a string representing hex values which requires 36 Bytes) and use virtual columns to actually calculate the real hex-string. So the original value is…

 
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Franck Pachot

12c dbms_stats.gather_table_stats on GTT do not commit

By | Oracle | No Comments

In my UKOUG OracleScene article on 12c online statistics and GTT I mentioned the following: A final note about those 12c changes in statistics gathering on GTT. In 11g the dbms_stats did a commit at the start. So if you did gather stats after the load, you had to set the GTT as ON COMMIT PRESERVE ROWS. Or you just vacuum what you’ve loaded. That has changed in 12c. If you now choose to do…

 
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Joël Cattin

Oracle 12cR2 : Optimizer Statistics Advisor

By | Database Administration & Monitoring, Database management, Development & Performance | No Comments

The Optimizer Statistics Advisor is a new Advisor in Oracle 12.2. The goal of this Advisor is to check the way you gather the statistics on your database, and depending on what is found, it will makes some recommendations on how you can improve the statistics gathering strategy in order to provide more efficient statistics to the CBO. This Advisor is also able to generate remediation scripts to apply the statistics gathering “best practices”. The…

 
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David Barbarin

SQL Server AlwaysOn availability groups and statistic issues on secondaries

By | Database Administration & Monitoring | 3 Comments

I would like to share with you an interesting issue you may face while using SQL Server AlwaysOn availability groups and secondary read-only replicas. For those who use secondary read-only replicas as reporting servers, keep reading this blog post because it is about update statistics behavior on the secondary replicas and as you may know cardinality estimation accuracy is an important part of the queries performance in this case. So a couple of days ago,…

 
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Franck Pachot

Rolling Invalidate Window Exceeded

By | Database Administration & Monitoring | 4 Comments

Today I was doing a hard parse storm post-mortem analysis. One hypothesis was rolling invalidation causing invalidation, but figures didn’t match. I often reproduce the hypothesis to check the numbers to be sure I interpret them correctly. Especially the timestamps in V$SQL_SHARED_CURSOR.REASON. And as it may help others (including myself in the future) I share the test case.  

 
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Nicolas Jardot

UKOUG 2012: Day 1 – Oracle 12c features and database performance

By | Technology Survey | No Comments

Today was the official launch of UKOUG 2012. We started with keynotes including one from Tom Kytes giving information about Oracle 12c features. Then I had some very interesting sessions on database performance. Oracle 12c When we talk about performance issues on SQL statement, it’s really often due to bad/missing statistics and Oracle using the wrong execution plan. In next Oracle database two features may (or not) help us to deal with this topic: Enhanced statistics…

 
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Stéphane Haby

Stéph@TechEd 2012: Episode 1 – the Pre-Conf. Seminar

By | Technology Survey | No Comments

This morning, I was very happy to go to my first TechEd. Between the 10 seminars, as I said yesterday, I started with SQL Server 2008R2/2012 performance, tuning and optimization session. The thing is that we had just one session for the whole day. I will not copy the presentation of the 2 speakers (Thomas LaRock and Denny Cherry) who presented remarkably this session despite the failure of air conditioning during the morning. Fortunately, it…

 
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Yann Neuhaus

How to retrieve previous table statistics using Oracle dbms_stats

By | Application integration & Middleware | 4 Comments

Sometimes, you need to modify the statistics of a table. There are various reasons: either for the performance analysis or because the execution plan changed. Oracle offers two methods: statistics restore or statistics export. Both are in the dbms_stats package. 1. Statistics restore This method uses the procedure dbms_stats.restore_%_stats, where % can be table, schema, database, and fixed_objects. This is an example for a restoration of a table with definite timestamp. The starting situation is:…

 
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Grégory Steulet

Saving time and increasing service availability with MySQL Enterprise Monitor 2.3

By | Hardware & Storage | 3 Comments

Nowadays MySQL Databases are encapsulated into many mission critical software solutions. Lots of companies host one or many MySQL databases in their data center, sometimes even without knowing it except when the MySQL service is no more available. In order to increase this service availability it is mandatory to have a monitoring solution. Regardles of you are using MySQL Server, MySQL replication or cluster the Oracle/MySQL monitoring solution is called MySQL Enterprise Monitor.

 
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