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Oracle OCP 1Z0-050（22题）解析
QUESTION 22:
Evaluate the following command:
SQL>ALTER SYSTEM SET db_securefile = 'IGNORE';
What is the impact of this setting on the usage of SecureFiles?
A. It forces SecureFiles to be created even if the BASICFILE option is specified to create the LOB.
B. It forces BasicFiles to be created even if the SECURE FILE option is specified to create the LOB.
C. It does not allow the creation of SecureFiles and generates an error if the SECUREFILE option is specified to create the LOB.
D. It ignores the SECUREFILE option only if a Manual Segment Space Management tablespace is used and creates a BasicFile.
正确答案：B
解析：
参考Oracle官方文档：
Beginning with Oracle Database 11g Release 1, Oracle introduced SecureFiles, a new LOB storage architecture. SecureFiles LOBs are created when the storage keyword SECUREFILE appears in the CREATE TABLE statement. The original LOB storage architecture, BasicFiles LOBs, is the default storage. It is in effect if the keyword SECUREFILE is not used, or if the keyword BASICFILE is used in the CREATE TABLE statement.
The initialization parameter db_securefile is set in the file init.ora.
The parameter db_securefile is of type text. Its allowable values are ALWAYS, PERMITTED [default], NEVER, or IGNORE. The db_securefile parameter is dynamic and its scope is ALTER SYSTEM.
Example 4-26 Setting db_securefile parameter through ALTER SYSTEM
ALTER SYSTEM SET db_securefile = 'ALWAYS';
The db_securefile parameter enables the database administrator to either allow SecureFiles LOBs to be created (PERMITTED), disallow SecureFiles LOBs from being created in the future (NEVER), attempt to create SecureFiles LOBs but fall back to BasicFiles LOBs (ALWAYS), or disallow SecureFiles LOBs and ignore any errors that would otherwise be caused by forcing BasicFiles LOBs with SecureFiles LOBs options (IGNORE).
If NEVER is specified, any LOBs that are specified as SecureFiles LOBs are created as BasicFiles LOBs. All SecureFiles LOB- specific storage options and features such as compress, encrypt, or deduplicate throw an exception. The BasicFiles LOB defaults are used for storage options not specified.
ALWAYS attempts to create all LOBs as SecureFiles LOBs but creates any LOBs not in ASSM tablespaces as BasicFiles LOBs, unless the SECUREFILE parameter is explicitly specified. Any BasicFiles LOB storage options specified are ignored, and the SecureFiles LOB defaults are used for all storage options not specified.
If IGNORE is specified, the SECUREFILE keyword and all SecureFiles LOB options are ignored.
可以使用ALTER SESSION 或者 ALTER SYSTEM 来修改这个初始化参数，语法如下：
DB_SECUREFILE = { NEVER | PERMITTED | ALWAYS | IGNORE }
参数的含义如下：
DB_SECUREFILE specifies whether or not to treat LOB files as SecureFiles.
Values:
NEVER
Any LOBs that are specified as SecureFiles are created as BasicFile LOBs. All SecureFile-specific storage options and features (for example, compress, encrypt, deduplicate) will cause an exception. The BasicFile LOB defaults will be used for storage options not specified.
PERMITTED
LOBs are allowed to be created as SecureFiles.
ALWAYS
Attempts to create all LOBs as SecureFile LOBs but creates any LOBs not in an Automatic Segment Space Managed tablespace as BasicFile LOBs, unless SECUREFILE is explicitly specified. Any BasicFile LOB storage options that are specified will be ignored and the SecureFile defaults will be used for all storage options not specified.
IGNORE
The SECUREFILE keyword and all SecureFile options are ignored.
If the COMPATIBLE initialization parameter is not set to 11.1.0 or higher, then LOBs are not treated as SecureFiles.
If there is a LOB column with two partitions (one that has a tablespace for which ASSM is enabled and one that has a tablespace for which ASSM is not enabled), then LOBs in the partition with the ASSM-enabled tablespace will be treated as SecureFiles and LOBs in the other partition will be treated as BasicFile LOBs.
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