Overflow must be monitored in secondary indexes, as well as in the primary tables. Even if the base table has a low overflow percentage, the secondary indexes can badly overflow. Except when the base table is a heap or B-tree table, the base table generally overflows before the secondary index.

Secondary indexes need to be monitored and modified at interim points--even between base table modifications--to ensure a low percentage of overflow pages. More information is provided in Modifying Secondary Indexes.