Helge,
You can stop the indexer by doing
<pre>
DELETE from search_observer_queue;
</pre>
which will remove all the items pending in the queue.
It also looks like you have a copy of OpenFTS 0.2 with a bug in it.
Check this thread: https://openacs.org/forums/message-view?message_id=52363
You best bet if you have that bug is to fix it, and restart the AOLserver which should allow the indexer to finish.
