统计信息动态采集级别的解释

enables dynamic sampling if all of the following conditions are true:

There is more than one table in the query.
Some table has not been analyzed and has no indexes.
The optimizer determines that a relatively expensive table scan would be required for this table that has not been analyzed.
The sampling levels are as follows if the dynamic sampling level used is from a cursor hint or from the optimizer_dynamic_sampling parameter:

Level 0: Do not use dynamic sampling.
Level 1: Sample all tables that have not been analyzed if the following criteria are met: (1) there is at least 1 unanalyzed table in the query; (2) this unanalyzed table is joined to another table or appears in a subquery or non-mergeable view; (3) this unanalyzed table has no indexes; (4) this unanalyzed table has more blocks than the number of blocks that would be used for dynamic sampling of this table. The number of blocks sampled is the default number of dynamic sampling blocks (32).
Level 2: Apply dynamic sampling to all unanalyzed tables. The number of blocks sampled is the default number of dynamic sampling blocks.
Level 3: Apply dynamic sampling to all tables that meet Level 2 criteria, plus all tables for which standard selectivity estimation used a guess for some predicate that is a potential dynamic sampling predicate. The number of blocks sampled is the default number of dynamic sampling blocks.
Level 4: Apply dynamic sampling to all tables that meet Level 3 criteria, plus all tables that have single-table predicates that reference 2 or more columns. The number of blocks sampled is the default number of dynamic sampling blocks.
Level 5: Apply dynamic sampling to all tables that meet the Level 4 criteria using 2 times the default number of dynamic sampling blocks.
Level 6: Apply dynamic sampling to all tables that meet the Level 5 criteria using 4 times the default number of dynamic sampling blocks.
Level 7: Apply dynamic sampling to all tables that meet the Level 6 criteria using 8 times the default number of dynamic sampling blocks.
Level 8: Apply dynamic sampling to all tables that meet the Level 7 criteria using 32 times the default number of dynamic sampling blocks.
Level 9: Apply dynamic sampling to all tables that meet the Level 8 criteria using 128 times the default number of dynamic sampling blocks.
Level 10: Apply dynamic sampling to all tables that meet the Level 9 criteria using all blocks in the table.
The sampling levels are as follows if the dynamic sampling level used is from a table hint:

Level 0: Do not use dynamic sampling.
Level 1: The number of blocks sampled is the default number of dynamic sampling blocks (32).
Level 2: The number of blocks sampled is 2 times the default number of dynamic sampling blocks.
Level 3: The number of blocks sampled is 4 times the default number of dynamic sampling blocks.
Level 4: The number of blocks sampled is 8 times the default number of dynamic sampling blocks.
Level 5: The number of blocks sampled is 16 times the default number of dynamic sampling blocks.
Level 6: The number of blocks sampled is 32 times the default number of dynamic sampling blocks.
Level 7: The number of blocks sampled is 64 times the default number of dynamic sampling blocks.
Level 8: The number of blocks sampled is 128 times the default number of dynamic sampling blocks.
Level 9: The number of blocks sampled is 256 times the default number of dynamic sampling blocks.
Level 10: Read all blocks in the table.