How missing statistics is handled in Oracle

When Oracle encounters a table with missing statistics, Oracle dynamically gathers the necessary statistics needed by the optimizer. Based on the settings of OPTIMIZER_DYNAMIC_SAMPLING parameter which is discussed in my previous topic optimizer gathers statistics and generate execution plan for the table with missing statistics.

Though in case of remote tables and external tables oracle does not perform dynamic sampling.

Whether dynamic sampling enabled or disabled the optimizer uses default values for its statistics.

The values are listed below.

A)Default Table Values When Statistics Are Missing
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1)Cardinality=num_of_blocks * (block_size - cache_layer) / avg_row_len
2)Average row length=100 bytes
3)Number of blocks=100 or actual value based on the extent map
4)Remote cardinality=2000 rows
5)Remote average row length=100 bytes

B)Default Index Values When Statistics Are Missing
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1)Levels=1
2)Leaf blocks=25
3)Leaf blocks/key=1
4)Data blocks/key=1
5)Distinct keys=100
6)Clustering factor=800