The RTREE_COST_ADJUST_VALUE environment variable
specifies a coefficient that support functions of user-defined data
types can use to estimate the cost of an R-tree index for queries
on UDT columns.
value
is a floating-point number, where 1 ≤ value ≤ 1000,
specifying a multiplier for estimating the cost of using an index
on a UDT column.
For spatial queries, the I/O overhead tends to exceed
by far the CPU cost, so by multiplying the uncorrected estimated cost
by an appropriate value from this setting, the database server
can make better cost-based decisions on how to implement queries on
UDT columns for which an R-tree index exists.