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

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:

• Exasol
• TOI

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:

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

• Exasol
• TOI

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.

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:

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.

This little script displays some useful meta-information:

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