Long running reorganize statements after cluster enlargement

Detail name	Value
Changelog Number	7996
Type	Bug
Status	Resolved
Affected Versions	Exasol 6.1.0
Fix Versions	Exasol 6.1.4
Resolution Date	2019-05-22

Description

We have discovered a performance bug in our system which manifests itself by very long execution times for REORGANIZE statements. The following conditions must be necessarily be met for the bug to manifest:

• Table with no distribution keys set
• Table has not yet been reorganized since last cluster enlargement.
• Unfavorable distribution of deleted marked rows

We stress that the bug occurs only in isolated cases and is very data specific - more precisely, the distribution of the deleted marked rows among the not deleted rows.

Workaround

As a workaround, distribution keys can be used as follows:

alter table <table> distribute by <some columns>;
reorganize table <table>;
alter table <table> drop distribution keys;