They have probably data from the spam comments. You could take a look and remove the unwanted data. Maybe you could disable the finder plugin for a while until you sort this out.

Ok ... how can i do that...!

To disable the finder plugin (smart search component) and prevent more entries you have to go to the Extensions Manager -> Plugins, select content type and disable the smart search plugin. You can also filter with type finder and disable all smart search plugins.

Check also the redirect table. Is this also large? If it is disable that as well. You can find it under System plugins.

I can't go to the back end of my site...!... I mean how can i do that from inside the database?

All plugins and extensions are under the _extensions table. There locate the ones I mention and choose to change their status.