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Database

Everything our consultants learn while running databases for customers: Oracle, PostgreSQL, SQL Server, MySQL, MariaDB, MongoDB and Delphix. Expect hands-on posts about installation, day-to-day administration, backup and recovery, performance tuning, replication and upgrades.

MySQL – Foreign keys and “Cannot delete or update a parent row: a foreign key constraint fails” error

As you know, foreign keys establish a sort of relationship between 2 tables. MySQL requires InnoDB storage engine to support foreign keys. In our example, we have the following parent table in a MySQL 5.7.21 server: mysqld3-(root@localhost) [sakila]> show create table actorG *************************** 1. row *************************** Table: actor Create Table: CREATE TABLE `actor` ( `actor_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,… 

EDB Failover Manager 3.0 and PostgreSQL 10.1

By Mouhamadou Diaw Edb Failover Manager edb-efm30 is now released and supports PostgreSQL 10.1. Efm is an EDB tool which can be used to perform a switchover and a failover in a PostgreSQL standby environment. In this blog we are going to see how we can install and configure efm in a standby environment. We suppose that the standby is… 

ODA – Reducing number of cores : Getting error DCS-10045

To perform some tests in order to determine the accurate number of cores to be used by the database application, I had to increase and decrease the number of CPU cores on an ODA using the DCS stack.  When increasing would never be a problem, decreasing number of CPU cores would fail into a DCS-10045 error. The ODA was initialized… 

18c new Lost Write Protection

By Franck Pachot . There are many layers between the Oracle Database pwrite() calls and the physical sector written on disk: filesystem, logical volume, SAN or NAS, with a lot of smart software running for Virtualisation, Compression, Snapshotting, Synchronisation… Are you sure that the changes you made to your data is actually persisted on disk, completely and without any corruption?… 

18c dbms_xplan note about failed SQL Plan Baseline

By Franck Pachot . SQL Plan Baselines is a great feature for plan stability: you capture the plans that you accept. However, if the data model changes and the accepted plans cannot reproduce, the optimizer will come with a new plan. In 18c we have a note from DBMS_XPLAN when the optimization ‘failed to use SQL plan baseline for this… 

ODA migration challenges: Non-OMF to OMF + 11.2.0.3 to 11.2.0.4

To do some application and performances tests, I had to copy a database from a third party Linux server to an ODA X7-2M. Looks pretty simple on the paper, but 2 small challenges came into the game. The first was that of course the source database was in Non-OMF while ODA works fully in OMF. The second was that the… 

ORA-12547 TNS lost contact on SLES12 and oracle 11.2.0.x

On a client’s site, I have migrated successfully Oracle 12c databases from RedHat to SLES12 without any problem. I encountered a problem doing the same work with Oracle 11.2.0.3 and oracle 11.2.0.4 on SLES 12. Once I have moved the database data files, redo logs, control files and spfile to the new server, when I try to startup the database,… 

18c, Cloud First and Cloud Only features: think differently

By Franck Pachot . Remember the times when the Oracle Software features were the same on all platforms? Where Oracle databases could be ported to any relevant platform? Where we were able to try any feature, freely, by downloading the latest release software? Now we need to think differently. Because: The new software is released on Cloud first The major… 

A free persistent Google Cloud service with Oracle XE

By Franck Pachot . In a previous post I’ve listed several free online services which run an Oracle XE so that you can test your SQL easily. You may want use Oracle XE further, with full access to the database and its host, and still from a web browser. You probably have a Google account. Then you also have a… 

PDB upgrade from 12c to 18c

By Franck Pachot . Oracle 18c is out, in the Oracle Cloud, and the first thing I do with a new version is testing how long it takes to upgrade a previous version PDB by unplug/plug. Faster upgrade should be the benefit of having a slim dictionary where the system objects are reduced to metadata links and data links. However,… 

Configuring huge pages for your PostgreSQL instance, Debian version

In the last post we had a look at how you can configure huge pages on RedHat and CentOS systems. For Debian and Debian based systems the procedure is different as Debian does not come with tuned. Lets see how it works there. Checking the basic system configuration works the same in Debian as in RedHat based distributions by checking…