RE: Full Text Index-2908MB Erik C. Brooks 29.Jun.06 12:35 PM Lotus Notes Domino Server 6.5.4 FP2Windows 2000
I found that late releases of R5 had much more stable indexes than ND6 does. I had some indexes that were 1GB + in R5 that would run stable for months, but on ND6 went belly-up every couple of weeks. Fortunately I was able to significantly trim my FT indexes down to reasonable sizes (200-300 MB).
If I were you I would open a ticket with Lotus Support so they can try to fix the issue. Chances are they'll be able to track it down quickly if it happens every few days, and it would help everybody that uses Domino.
Alternatively you could have an agent kill and re-create the index every few days, or set up a program document to run Updall to force a rebuild. Though I'm guessing it would take several hours to re-create the index each time.
Another option (albiet a ton of work) would be to re-architect your application a bit: remove non-needed fields, use archiving, spread the load to multiple databases, or something else to try to keep the overall DB sizes (and therefore FT index sizes) down.