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Category Archives: Oracle

Oracle Team

When to gather workload system statistics?

By | Database management, Oracle | 2 Comments

By Franck Pachot . This month we started to give our Oracle Tuning Workshop. And with a new workshop comes new questions. We advise to give to the optimizer the most accurate statsistics that we can have. That suggests that WORKLOAD statistics are better than NOWORKLOAD ones because they gather the average number of blocks read in multiblock read, rather than using default values. But then, the question is: which time period do you choose…

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Oracle Team

NLS_LANG on Windows in Europe: WE8MSWIN1252 or WE8PC850?

By | Database management, Oracle | 2 Comments

By Franck Pachot . In europe we have accents and non US7ASCII characters. We need special characterset. I’m not talking about Unicode here that solves all the problems. If you have a Java application, you have no problem: it’s Unicode. You can store all characters in one multi-byte characterset. But for other applications, on Windows, you have 2 possible charactersets for Western Europe WE8MSWIN1252 and WE8PC850. WE8MSWIN1252 is the one that is set by default…

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Oracle Team

SOUG-Romand: Journée performance le 21 mai

By | Database management, Oracle | No Comments

By Franck Pachot . (english below) Bonne nouvelle pour les francophones: le SOUG-R est de plus en plus actif. Le 21 mai 2015 une journée performance est organisée sur Lausanne. Mon call for paper a été accepté: je vous parlerais des SQL Plan Directives – une nouvelle fonctionnalité 12c accessible aussi en Standard Edition! Voici l’abstract: SQL Plan Directives – la mémoire de l’optimizeur L’optimiseur 12c peut évaluer la précision de son estimation, et se…

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Oracle Team

Flashback logging overhead: ‘db file sequential read’ on UNDO tablespace

By | Database Administration & Monitoring, Oracle | No Comments

By Franck Pachot . in my previous post I’ve reproduced an issue where some bulk insert into a GTT was generating too much undo. But the real case I encountered was worse: the insert was reading lot of UNDO. And lot of this undo was read from disk. Jonathan Lewis has pointed me to a possible explanation he has given (here) I’ve reproduced the testcase from the previous post after setting the database to do…

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Oracle Team

Insert into GTT: bulk with APPEND_VALUES

By | Database management, Oracle | No Comments

By Franck Pachot . This post is about the case I had where a GTT was generating too much undo. The effects were amplified by the fact that the database was in flashback logging (see Jonathan Lewis answer in my question on OTN forum about that, but that’s for the next post. Nothing here is specific to GTT, but generating undo (and the related redo) is even more awkward on GTT. Here is the query:…

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Oracle Team

Oracle multitenant dictionary: upgrade

By | Database management, Oracle | No Comments

By Franck Pachot . This is a second part of the previous post about metadata link. I’ve shown how a sharing=metadata function becomes a sharing=none function when it is changed in the pdb – i.e when not having the same DDL, not having a different signature. Here is another experimentation doing the opposite: change the function in root and see what happens in the pdb. Again playing with internals in order to understand the ‘upgrade…

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Oracle Team

Oracle multitenant dictionary: metadata links

By | Database management, Oracle | 2 Comments

By Franck Pachot . As in previous posts (1 and 2) I’m still playing with multitenant dictionary. You may wonder why I’m spending time to do unsupported things that we will never be able to use in real life. Of course, playing with internals is fun But it’s not only that. We will implement CDB databases (multi-tenant, and single-tenant as I think non-CDB will be deprecated in future versions). We will operate pluggable databases (clone,…

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Oracle Team

Happy New Year 27, 104, 2015 and 2558

By | Database management, Oracle | No Comments

By Franck Pachot . calendar today tomorrow message —————– —— ——— ————– Arabic Hijrah 1436 1436 English Hijrah 1436 1436 Gregorian 2014 2015 Happy New Year Japanese Imperial 0026 0027 Happy New Year Persian 1393 1393 ROC Official 0103 0104 Happy New Year Thai Buddha 2557 2558 Happy New Year   According to Oracle calendars… SQL> l 1 with cal as ( 2 select ‘Arabic Hijrah’ name from dual union all select ‘English Hijrah’ from…

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Oracle Team

Oracle multitenant dictionary: object links

By | Database management, Oracle | 3 Comments

By Franck Pachot . I’ve described Oracle 12c metadata and object links internals in a previous post. But before that, the first time I investigated on it, I made a wrong assumption because I was looking at AUDIT_ACTIONS which is not correctly implemented. That investigation came from a question on dba-village. And recently Ivica Arsov (@IvicaArsov) has made an interesting comment about AUDIT_ACTIONS object link table, so I’ll explain here what is special with it….

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Oracle Team

Creating a schema synonym in Oracle – an unsupported feature

By | Database management, Oracle | 3 Comments

By Franck Pachot . Ivica Arsov (@IvicaArsov) has made an interesting comment about AUDIT_ACTIONS object link table. I’ll blog about it soon, but in the meantime when checking its definition in cataudit.sql it came upon the following: /* SCHEMA SYNONYMS will be added in 12g */ — insert into audit_actions values (222, ‘CREATE SCHEMA SYNONYM’); — insert into audit_actions values (224, ‘DROP SCHEMA SYNONYM’); which caught my attention. So this blog post is not about…

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