Shulou(Shulou.com)06/01 Report--

The way of accessing data blocks through ROWID BATCHED is added in Oracle 12c, which optimizes the resource consumption and scanning times of data blocks caused by the original way of accessing data blocks using a single rowid, that is, TABLE ACCESS BY INDEX ROWID BATCHED features. This feature is controlled by hiding the parameter "_ optimizer_batch_table_access_by_rowid". The default value is true, which is enabled by default.

The following is part of the execution plan for SELECT * FROM employees WHERE employee_id > 190;.

| | Id | Operation | Name | Rows | Bytes | Cost (% CPU) | Time |

| | 0 | SELECT STATEMENT | 2 (100) | |

| | 1 | TABLE ACCESS BY INDEX ROWID BATCHED | EMPLOYEES | 16 | 1104 | 2 (0) | 00:00:01 |

| | * 2 | INDEX RANGE SCAN | EMP_EMP_ID_PK | 16 | | 1 (0) | 00:00:01 |

Predicate Information (identified by operation id):

2-access ("EMPLOYEE_ID" > 190)

Step 2 of the above execution plan shows a range scan of the emp_emp_id_pk index on the hr.employees table. The database uses the rowid obtained from the index to find the corresponding rows in the employees table and then retrieve them. Step 1 shows that for BATCHED access using the rowid retrieved from the index, the database sorts the rowid retrieved from the index and then accesses the rows in block order, thus reducing the number of blocks that the database must access to reduce resource consumption.

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