Infrastructure at your Service

Category

Development & Performance

David Barbarin

RCSI with foreign keys, NULL values and paramater sniffing behavior

By | Development & Performance, SQL Server | No Comments

In this blog post let’s go back to the roots (DBA concern) with a discussion with one of my friends about a weird transaction locking issue. In fact, this discussion was specifically around two questions. The first one was why SQL Server continues to use shared locks in RCSI mode leading to blocking scenarios and the second one was about compiled objects with weird NULL value parameter sniffing behavior. This discussion was very funny for…

Read More
Petre Radut

When you change the UNDO_RETENTION parameter, the LOB segment’s retention value is not modified

By | Database Administration & Monitoring, Database management, Development & Performance, Hardware & Storage, Oracle | No Comments

Below, I will try to explain, a particular case for the general error : ORA-01555 snapshot too old error.. Normally, when we have this error, we are trying to adapt the retention parameters or to tune our queries. SQL> show parameter undo; NAME TYPE VALUE ———————————— ———– —————————— temp_undo_enabled boolean FALSE undo_management string AUTO undo_retention integer 3600 –extended from 900, undo_tablespace string UNDOTBS1 But, are some scenarios where the above rule is not working . We…

Read More
Lazhar Felahi

SQL Tuning – Mix NULL / NOT NULL Values

By | Development & Performance, Oracle | No Comments

One of the difficulty when writing a SQL query (static SQL) is to have in the same Where Clause different conditions handling Null Values and Not Null Values for a predica. Let’s me explain you by an example : Users can entered different values for a user field from an OBI report: – If no value entered then all rows must be returned. – If 1 value entered then only row(s) related to the filter…

Read More
Petre Radut

Recover a corrupted datafile in your DataGuard environment 11G/12C.

By | Database Administration & Monitoring, Database management, Development & Performance, Oracle | No Comments

On a DG environment, a datafile needs to be recovered on the STANDBY site, in two situations : when is deleted or corrupted. Below, I will explain  how to recover a corrupted datafile, in order to be able to repair the Standby database, without to be necessary to restore entire database. Initial situation : DGMGRL> connect / Connected to “PROD_SITE2” Connected as SYSDG. DGMGRL> show configuration; Configuration – CONFIG1 Protection Mode: MaxPerformance Members: PROD_SITE2 -…

Read More
Pierre-Yves Brehier

DOAG 2018 – What to learn from a battle on IT technologies?

By | Development & Performance | No Comments

This year’s my 6th participation with dbi services at the DOAG Conference + Exhibition Nuremberg (as a “non-techie” attendee, no need to say), but it was my very first battle on IT technologies. And it was fun! On the DOAG 2018 Conference + Exhibition DOAG 2018 Conference + Exhibition is taking place November 20 – 23, 2018 in Nuremberg. Participants have the opportunity to attend a three-day lecture program with more than 400 talks and…

Read More
Christophe Cosme

Pass summit – day 4

By | Big Data, Business Intelligence, Cloud, Database Administration & Monitoring, Development & Performance | No Comments

Optimizing Multi-Billion Row Tables in Tabular in 2018   I wanted to attend the session moderated by Marco Russo to see his approach of optimizing performance in Tabular model The first thing to understand is how the data is stored and organized in a Tabular model. It is of course using the xVelocity in-memory capabilities with the Vertipac column storage layout engine. It organizes the data, compressing  it by column,  in combination with a dictionary…

Read More
Cesare Cervini

A SQLite extension for gawk (part II)

By | Development & Performance, Entreprise content management | No Comments

Welcome to part II of a three-part article on extending gawk with a SQLite binding. Part I is here. Part II is followed by Part III, which give some explanations for the code presented here and shows how to use the extension with a stress test. Here, I’ll list the source code of the extension and give instructions to compile and use it in gawk. Beware though that the code should be taken with several…

Read More
Cesare Cervini

An SQLite extension for gawk (part I)

By | Development & Performance, Entreprise content management | No Comments

Quick: what is the most used database management system on our planet ? Oracle ? Wrong. SQL server ? Wrong again ! MySQL ? You’re almost there. It’s SQLite. Surprised ? I must confess that I was too. Actually, SQLite is special in that it is not the traditional 2-tiers client/server but one-tier and embedded, which means that it works as a library linked to an application. As such, it is used to fulfill the…

Read More
Stéphane Haby

SQL Server Tips: How many different datetime are in my column and what the delta?

By | Database management, Development & Performance, SQL Server | No Comments

Few months ago, a customer asks me for finding in a column, how many rows exist with the same date & time and the delta between them. The column default value  is based on the function CURRENT_TIMESTAMP and used as key as well. This is obviously a very bad idea but let’s go ahead… This anti pattern may lead to a lot of duplicate keys and the customer wanted to get a picture of the…

Read More
David Barbarin

SQL Server on Linux – I/O internal thoughts

By | Database management, Development & Performance, SQL Server | 2 Comments

Let’s start the story from the beginning with some funny testing I tried to perform with SQL Server on Linux a couple of months ago. At that time, I wanted to get some pictures of syscalls from SQL Server as I already did in a past on Windows side with sysinternal tools as procmon and stack traces. On Linux strace is probably one of the best counterparts. Firstly, please note this blog is just from…

Read More