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Franck Pachot

Franck Pachot

19c: scalable Top-N queries without further hints to the query planner

By | Oracle | No Comments

By Franck Pachot . The FETCH FIRST … ROWS ONLY syntax arrived in Oracle 12c and is much more convenient than using a subquery with ‘ORDER BY’ wrapped in a “WHERE ROWNUM < …” around it. But as I mentioned in a previous post it required the FIRST_ROWS() hint to get correct estimations. In SQL you don’t want to overload your code for performance, right? The RDBMS optimizer does the job for you. This was…

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Franck Pachot

The myth of NoSQL (vs. RDBMS) “joins dont scale”

By | AWS, Database Administration & Monitoring, NoSQL, Oracle, Postgres, SQL Server | 15 Comments

By Franck Pachot . I’ll reference Alex DeBrie article “SQL, NoSQL, and Scale: How DynamoDB scales where relational databases don’t“, especially the paragraph about “Why relational databases don’t scale”. But I want to make clear that my post here is not against this article, but against a very common myth that even precedes NoSQL databases. Actually, I’m taking this article as reference because the author, in his website and book, has really good points about…

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Franck Pachot

Oracle ACFS: “du” vs. “df” and “acfsutil info”

By | Oracle | No Comments

By Franck Pachot . This is a demo about Oracle ACFS snapshots, and how to understand the used and free space, as displayed by “df”, when there are modifications in the base parent or the snapshot children. The important concept to understand is that, when you take a snapshot, any modification to the child or parent will [[email protected] ~]$ asmcmd lsdg DATAC1 State Type Rebal Sector Logical_Sector Block AU Total_MB Free_MB Req_mir_free_MB Usable_file_MB Offline_disks Voting_files…

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Franck Pachot

Oracle Autonomous Linux: cron’d ksplice and yum updates

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

By Franck Pachot . Oracle Enterprise Linux (OEL) is a Linux distribution which is binary compatible with Red Hat Enterprise Linux (RHEL). However, unlike RHEL, OEL is open source, free to download, free to use, free to distribute, free to update and gets free bug fixes. And there are more frequent updates in OEL than in CentOS, the free base of RHEL. You can pay a subscription for additional support and features (like Ksplice or…

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Franck Pachot

The Oracle ACE program ♠ what it is not ♠

By | Database Administration & Monitoring | 4 Comments

By Franck Pachot . I had a few questions about the Oracle ACE program recently and I thought about putting some answers there. Of course, that’s only my point of view, there’s an official web page: https://www.oracle.com/technetwork/community/oracle-ace/index.html The program is flexible and open, with a large diversity of people, technologies, contributions, levels,… Then rather than explaining what it is, which would be limiting, I’ll rather tell you… what it is not. It is not a…

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Franck Pachot

Some myths about PostgreSQL vs. Oracle

By | Oracle, Postgres | One Comment

By Franck Pachot . I originally wrote this as a comment on the following post that you may find on internet: https://www.2ndquadrant.com/en/blog/oracle-to-postgresql-reasons-to-migrate/ but my comment was not published (many links in it… I suppose it has been flagged as spam?) so I put it there. You should never take any decision on what you read on the internet without verifying. It is totally valid to consider a move to Open Source databases, but doing it…

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Franck Pachot

Oracle non-linguistic varchar2 columns to order by without sorting

By | Cloud, Oracle | No Comments

By Franck Pachot . Sorting data is an expensive operation and many queries declare an ORDER BY. To avoid the sort operation you can build an index as it maintains a sorted structure. This helps with Top-N queries as you don’t have to read all rows but only those from a range of index entries. However, indexes are sorted by binary values. For NUMBER or DATE datatypes, the internal storage ensures that the order is…

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Franck Pachot

No{Join,GroupBy}SQL – Analytic Views for BI

By | Cloud, Oracle | No Comments

By Franck Pachot . Advocates of NoSQL can query their structures without having to read a data model first. And without writing long table join clauses. They store and query a hierarchical structure without the need to follow relationships, and without the need to join tables on a foreign key name, in order to get a caption or description from a lookup table. The structure, like an XML or JSON document, provides metadata to understand…

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Franck Pachot

Oracle 12c – global partial index

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

By Franck Pachot . We have an incredible number of possibilities with Oracle. Yes, an index can be global (indexing many partitions without having to be partitioned itself on the same key) and partial (skipping some of the table partitions where we don’t need indexing). In the previous post of this series of small examples on recent features I partitioned a table, with covid-19 cases per day and per country, partitioned on range of date…

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Franck Pachot

Oracle 12c – reorg and split table with clustering

By | Cloud, Database Administration & Monitoring, Oracle | 2 Comments

By Franck Pachot . In this series of small examples on recent features, I have imported in a previous post, the statistics of covid-19 per day and per countries. This is typical of data that comes as a time-series ordered by date, because this is how it is generated day after day, but where you probably want to query from another dimension, like per countries. If you want to ingest data faster, you keep it…

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