Difficult to delete old PIQ system alerts

Target : We are trying to delete old PIQ alerts .

Reason: Table size will be reduced as effect of deletion hence DB size
will be reduced and performance will be improved.

Unable to delete PIQ system old alert.
We are unable to delete old PIQ alert beyond 505 days.Whenever we are
trying to do so , we get dump "System_No_Roll".

We log into PIQ system , run Tcode SE38 and run report RSALERTPROC .
Thereafter we select no. of days old and run report.We decreased the no
of days for deletion of alert gradually to prevent dump , to the extent
of a single day ,still dump faced.

Also we tried to run Background job for same , it got cancelled.