Ralf on "Search Cache"

Hi,

i have noticed that the table 'search_cache' becomes fairly large over the day.
The Cache setting for the Search is set to 15 minutes.
In the search_cache table entries are stored which are older than this 15 minutes.
When I hit the 'database optimisation' button (in german Datenbank aktualisieren) the search_cache table gets empty.

My question:
Do i have manually hit the 'Datenbank aktualisieren' each time when the search_cache table gets to large or is there a kind of autmatism which optimizes the table?

Cheers
Ralf