Join Index Costs Summary
Creation and maintenance costs for join indexes can be a resource burden because of
their processing overhead. In the case of join index maintenance, the burden is an
ongoing process that lasts for the life of the index.
Costs vary considerably among the various types of joins used as well as between simple
and aggregate types. The following bulleted list summarizes the conclusions to be
drawn from the performance analyses performed.
Maintenance overhead for in-place aggregate join indexes ranges from 1.0 to 2.9.
Maintenance overhead for aggregate join indexes that redistribute rows ranges from
2.6 to 9.5.
Maintenance overhead for simple join indexes ranges from 1.0 to 23.1, increasing as
the number of hits per data block increases.
Maintenance overhead for aggregate join indexes decreases as the number of hits per
data block increases because of the efficiencies of block-at-a-time operations in
the file system.
Maintenance overhead for insert operations is significantly less than the maintenance
overhead required for update and delete operations.