Small table replication performance fixes and improvements

Detail name	Value
Changelog Number	6664
Type	Improvement
Status	Resolved
Fix Versions	Exasol 6.1.0
Resolution Date	2018-09-13

Background
The technique of small table replication significantly improves join performance. With EXASOL-1798 the replication costs have been reduced and hence much larger system replication borders were supported (SOL-101).
Nevertheless, it turned out that replicating tables can degrade the performance of certain query types (performance anomalies).

Improvement
The optimizer decisions regarding table replication have been improved so that the optimizer:

• avoids replicating all tables of a pipeline even if they are small (every node would compute everything)
• avoids replicating medium sized tables that have been written (no fast table replication possible)
• ignores replication table size borders as smart table replication operates column-wise

Benefit
Improved performance in corner cases when replication border is increased.

Changed behavior