Technical Exasol

How to use Exasol’s Automatic Table Reorganization

17 Sep 2019 | Share

Exasol Blog - How to use Exasol's Automatic Table Reorganization

One of Exasol’s key features is the low maintenance effort when compared to many other database systems. Automatic Table Reorganization is one example:

Exasol offers CREATE OR REPLACE TABLE and the DELETE_PERCENTAGE is zero after the table is created. The TABLE_ROW_COUNT is maintained automatically after each data manipulation language (DML) – there’s no need to gather statistics.

10% of rows are marked as deleted for this table but not yet removed. Let’s delete another 100,000 rows and see what happens.

Now 20% of rows are marked as deleted. There’s a threshold of 25% deleted rows that triggers an automatic reorganization:

DELETE_PERCENTAGE resets to zero because of the automatic reorganization – I didn’t have to do anything.

By the way, if INSERTS follows the DELETE, the DELETE_PERCENTAGE decreases automatically too as the space used by the rows marked as deleted is used.

Reorganization can be done manually too:

Uwe Blog Code 6

A manual reorganization is possible but usually isn’t necessary. Typically, reorganization is only needed after the Exasol cluster has been enlarged by adding one or more nodes.

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