Oracle calculates the cost for each candidate of execution plan. This cost calculation depends on the many different factors. Below are the oracle cost calculation factors
1. Object Statistics:
Object statistics is the most important thing in the cost calculation for oracle. These statistics include the number of blocks in the table, number of rows in the
tables, avg row length, column statistics etc. Oracle uses these statistics to create the efficient execution plans.
2. Database Parameters:
Cost of the execution plan is depends on many configuration parameters. These parameters determine that how many blocks can be read in IO operations, how much memory
can be allocated to sorting and hashing, whether to use hash join or nested loops joins etc.
3. System Statistics:
System statistics gives guidance to optimizer related to CPU and IO rates which helps optimizer in cost calculations.