Improve MERGE statement with large target tables and many duplicates
Details
| Detail name | Value |
|---|---|
| Changelog Number | 7202 |
| Type | Improvement |
| Status | Open |
Problem Description
In 6.0.0 we introduced MERGE enhancements for large target tables (see EXASOL-1788). This allows Exasol to choose between two MERGE-mechanisms with different performance aspects.
However, there are a few border cases where the decision by the optimizer leads to far slower MERGE-statements. That may happen if the join condition between source and target table has very many duplicates both in the source and the target table. That problem might also occur for rows that were already deleted in the target table but not completely purged from the indices, yet.
Improvement
We will improve the optimizer to work better with cases where the join between source and target table will create more rows than the target table has.
