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Category Archives: Database Administration & Monitoring

Franck Pachot

Oracle 12.1.0.2: Wait event histograms in μs

By | Database Administration & Monitoring, Oracle | 2 Comments

When an Oracle Database spends a high percentage of its DB time in User I/O, I usually check the wait event histograms in order to see if the storage system is working well. But today, with storage going to SSD, most I/O are less than 1 milliseconds and we have no details about those wait times. Here is what is exposed by V$WAIT_EVENT_HISTOGRAM:   select event,wait_time_milli,wait_count from v$event_histogram where event like ‘db file sequential read’…

 
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Franck Pachot

Linux: how to monitor the nproc limit

By | Database Administration & Monitoring, Oracle | 14 Comments

You probably know about ‘nproc’ limits in Linux which are set in /etc/limits.conf and checked with ‘ulimit -u’. But do you know how to handle the monitoring and be alerted when you’re close the fixed limit? Nproc and ps Nproc is defined at OS level to limit the number of processes per user. Oracle 11.2.0.4 documentation recommends the following: oracle soft nproc 2047 oracle hard nproc 16384 But that is often too low, especially when…

 
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Franck Pachot

Oracle Exadata – poor optimization for FIRST_ROWS

By | Database Administration & Monitoring, Oracle | 3 Comments

In a previous blog, I discussed the difference between rownum and row_number(), in particular their behaviour in implicitely adding a first_rows(n) to the optimizer. That reminded me that I forgot to blog about an issue I encountered and which concerns both approaches. It was on an Exadata: a nice full table scan with smartscan was taking a long time. And forcing to an index access – with a very bad index – was better. The…

 
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Franck Pachot

Best practice for the sending of an Oracle execution plan

By | Database Administration & Monitoring, Oracle | 5 Comments

You have a query that takes too long and you want help to analyze the execution plan? Then you need to get it with relevant information, and correctly formatted. Autotrace is not a good option as it does not bind the variables in the same way as your application. Explain plan only shows estimations, but if we have a performance issue, this probably means that the estimation is wrong. I prefer SQL Monitoring when we…

 
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Franck Pachot

Archivelog deletion policy for Standby Database in Oracle Data Guard

By | Database Administration & Monitoring, Oracle | 39 Comments

Do you use ARCHIVELOG DELETION POLICY TO APPLIED ON ALL STANDBY for your Oracle databases in Data Guard? Maybe you also use the Fast Recovery Area as archive log destination. That’s good practice! But did you ever check that it works as expected? What I mean is this: The archived logs that you don’t need are reclaimable by the FRA when space is needed And the archived logs that are required for availability (standby or…

 
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Stéphane Haby

SQL Server 2012: First Hotfix for Service Pack 1 available

By | Database Administration & Monitoring | No Comments

This month, Microsoft has released the first hotfix for SQL Server Service Pack 1. Analysis This Hotfix concerns the installation of SQL Server components and Analysis Services. If you have installed the RTM version with Analysis Service and successfully installed Service Pack 1, you may experience problems in the next installation process for other component: The installation freezes and does not finish. Problem Windows Installer tries to repair the installation and then blocks the next…

 
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Stéphane Haby

SQL Server 2012: Feature Pack

By | Database Administration & Monitoring | 2 Comments

Since the third CTP version of SQL Server 2012 codename Denali, you have some features available to provide an additional value for Microsoft® SQL Server 2012 like the other SQL Server versions. This Feature Pack or Manageability Tool Kit are available but are not the final version. I have compiled all information in this blog to find it easily.

All DBA should know that Feature Pack exists, how to find it and of course use it.Wink

 
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Stéphane Haby

Diving into Databases

By | Database Administration & Monitoring | 3 Comments

By dbi services, we are a few poeples passionate by diving.
We take this opportunity to let you dive into the two databases lakes Oracle and SQL server and see their similarities and differences. For this first level of diving (named ODD), we will not going too deep and not have narcosis or

databases toxicity.
As always, we’ll start with a short briefing to present the environment and the different themes.
Have a nice dive !

 

“BRIEFIIING !”

 
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