TOI

Uwe Hesse's picture

Automatic Indexes in #Exasol

An Exasol database will automatically create, maintain and drop indexes, following the core idea to deliver great performance without requiring much administrative efforts. Like our tables, our indexes are always compressed and you don’t need to configure anything for that.

Joins between two or more tables are processed like this in Exasol: One table is full scanned (this is called the root table) and the other tables are joined using an index on their join columns.

If these indexes on the join columns are not already existing, they are automatically created during the join operation. Taking two tables t1 and t2 as an example, and a statement like

Uwe Hesse's picture

Comparison between #Oracle and #Exasol

After having worked with both databases for quite some time, this is what I consider to be the key differences between Oracle and Exasol. Of course the two have much in common: Both are relational databases with a transaction management system that supports the ACID model and both follow the ANSI SQL standard – both with some enhancements. Coming from Oracle as I do, much in Exasol looks quite familiar. But let’s focus on the differences:

Strengths

Oracle is leading technology for Online Transaction Processing (OLTP). If you have a high data volume with many users doing concurrent changes, this is where Oracle shines particularly.

Exasol is leading technology for analytical workloads. If you want to do real-time ad hoc reporting on high data volume, this is where Exasol shines particularly.

Uwe Hesse's picture

Recover dropped tables with Virtual Access Restore in #Exasol

The technique to recover only certain objects from an ordinary backup is called Virtual Access Restore. Means you create a database from backup that contains only the minimum elements needed to access the objects you request. This database is then removed afterwards.

Let’s see an example. This is my initial setup:

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Uwe Hesse's picture

Understanding Partitioning in #Exasol

Exasol introduced Partitioning in version 6.1. This feature helps to improve the performance of statements accessing large tables. As an example, let’s take these two tables:

 

Uwe Hesse's picture

Accelerate your #BI Performance with #Exasol

Your BI users complain about slow performance of their analytical queries? Is this your Status Quo?

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Uwe Hesse's picture

Account locking in an Active Data Guard environment

During the Data Guard round table of the excellent UKOUG Tech18 conference I got aware of this topic that I’d like to share with the Oracle community:

What is the locking behavior for user accounts in an environment where users may connect to the primary as well as to the standby database?

Uwe Hesse's picture

#DOAG2018 Impressions

As every year in November, the database circus moved to Nuremberg on behalf of the annual DOAG conference. As you may know, this conference has very high standards in terms of turnout and top-notch speakers and it reached them once again: It was a great event!

It started with the welcome keynote where Stefan Kinnen told us that the conference attracted over 2000 attendees and more than 400 speakers from all over the world. That should make it the largest database conference in Europe, I suppose!

Uwe Hesse's picture

Installing an #Exasol 6.1 Cluster on VirtualBox

After having installed the latest VirtualBox version, an ISO file with the latest Exasol version has to be downloaded. The machine hosting VirtualBox should have at least 16 GB RAM and 80 GB free disk space in order to run a 2+1 Cluster with 3 data nodes and one license server. I’m doing it on my Windows 10 notebook.

Uwe Hesse's picture

Understanding Distribution in #Exasol

Exasol doesn’t need much administration but getting distribution right matters

Exasol uses a clustered shared-nothing architecture with many sophisticated internal mechanisms to deliver outstanding performance without requiring much administration. Getting the distribution of rows between cluster nodes right is one of the few critical tasks left, though. To explain this, let’s say we have two tables t1 and t2:

Uwe Hesse's picture

Using the Query Cache for good performance in #Exasol

The result of a query can be cached in Exasol to the effect that repeated identical queries complete in no time. This feature has been introduced in version 5 and is enabled by default.

SQL_EXA> select session_value,system_value  from exa_parameters where parameter_name='QUERY_CACHE';
EXA: select session_value,system_value  from exa_parameters where parameter...

SESSION_VALUE        SYSTEM_VALUE
-------------------- --------------------
ON                   ON

1 row in resultset.

The Query Cache can be (de-)activated on the session level as well as on the system level.

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