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Category Archives: Oracle

Oracle Team

Oracle EM agent 12c thread leak on RAC

By | Database management, Oracle | 4 Comments

By Franck Pachot . In a previous post about nproc limit, I wrote that I had to investigate the nproc limit with the number of threads because my Oracle 12c EM agent was having thousands of threads. This post is a short feedback about this issue and the way I have found the root cause. It concerns the enterprise manager agent 12c on Grid Infrasctructure >= 11.2.0.2 NLWP The issue was: ps -o nlwp,pid,lwp,args -u…

 
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Oracle Team

Partial Join Evaluation in Oracle 12c

By | Database management, Oracle | One Comment

By Franck Pachot . Do you think that it’s better to write semi-join SQL statements with IN(), EXISTS(), or to do a JOIN? Usually, the optimizer will evaluate the cost and do the transformation for you. And in this area, one more transformation has been introduced in 12c which is the Partial Join Evaluation (PJE). First, let’s have a look at the 11g behaviour. For that example, I use the SCOTT schema, but I hire…

 
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Oracle Team

Oracle Parallel Query: Did you use MapReduce for years without knowing it?

By | Database management, Oracle | No Comments

By Franck Pachot . I’ve read this morning that MapReduce is dead. The first time I heard about MapReduce was when a software architect proposed to stop writing SQL on Oracle Database and replace it with MapReduce processing. Because the project had to deal with a huge amount of data in a small time and they had enough budget to buy as many cores as they need, they wanted the scalability of parallel distributed processing….

 
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Oracle Team

Linux: how to monitor the nofile limit

By | Operation systems, Oracle | One Comment

By Franck Pachot . In a previous post I explained how to measure the number of processes that are generated when a fork() or clone() call checks the nproc limit. There is another limit in /etc/limits.conf – or in /etc/limits.d – that is displayed by ‘ulimit -n’. It’s the number of open files – ‘nofile’ – and here again we need to know what kind of files are counted. nofile ‘nofile’ is another limit that…

 
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Oracle Team

Linux: how to monitor the nproc limit

By | Database Administration & Monitoring, Oracle | 16 Comments

By Franck Pachot . 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…

 
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Oracle Team

How to list all Oracle system schemas

By | Database management, Oracle | 4 Comments

By Franck Pachot . Do you want to know which users come with the Oracle Database and which are the ones you have created? This is that not easy, especially prior to Oracle 12c. You know SYS and SYSTEM, but there are many others – especially when you have installed all options. And it is important to know them all, e. g. when you import or apply a password policy, etc. Let’s see the options…

 
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Oracle Team

Oracle Exadata – poor optimization for FIRST_ROWS

By | Database Administration & Monitoring, Oracle | 3 Comments

By Franck Pachot . 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…

 
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Oracle Team

Oracle 12c extended datatypes better than CLOB?

By | Database management, Oracle | 6 Comments

By Franck Pachot . 12c has introduced character strings that can can go above 4000 bytes. In the previous versions, in PL/SQL only we were allowed to have VARCHAR2 up to 32k. In SQL the VARCHAR2 datatype was limited to 4000 and CHAR was limited to 2000. That became a bit small especially when lot of applications needed to store unicode characters. From 12c we can have SQL datatypes having up to 32k bytes for…

 
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Oracle Team

Oracle SQL Monitoring reports in flash, html, text

By | Database management, Oracle | No Comments

By Franck Pachot . I have recently posted on the way I like to extract execution plans. When we have Tuning pack, I suggest to get them with SQL Real-Time Monitoring as an active report. However, Martin Preiss said in a comment that he prefers the text format – easier to search, copy, and paste. And that’s a very good remark. We still need plain text. My point is that if you send me the…

 
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Oracle Team

Exploring Oracle SE & EE performance statistics with Orachrome Lighty

By | Database management, Oracle | No Comments

By Franck Pachot . At dbi services, we really like Lighty for Oracle, a tool which helps exploring performance statistics whether they originate from AWR (available only in Enterprise Edition with Diagnostic Pack option) or from Statspack (available via Standard Edition). As a matter of fact, we like it so much that we have became Orachrome Partner. If you want to try it out for yourselves, there is a free trial here. If you have…

 
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