Hi Franco,
this is the internal database of the SEO Toolkit. Are you using the extension actively? If not, then you can uninstall it and the database file will be removed as well.
If you are using the SEO Toolkit, then you cannot do much in terms of reducing the database manually. How many domains do you have on this server? Are they high-traffic websites? My assumption is that you have a huge dataset for the Log File Analyzer (many visits from search engine bots) on these domains.
I absolutely see the problem here and we will discuss the possibility to clean up the database from the extension interface internally.
Cheers
Viktor