Oracle教程 2023-02-24

Oracle 视图 V$SYSTEM_PARAMETER 官方解释，作用，如何使用详细说明

本站中文解释

Oracle视图V$SYSTEM_PARAMETER主要用来查看系统参数和当前会话的参数的值。在Oracle数据库参数的存储方式不同，基本上分为三类：

1、instance参数；影响整个实例/数据库的参数值, 包含在v$parameter表或SPFILE文件，只能在实例管理下更改，但在会话级别上仍可查看其值。

2、session参数：影响特定会话的参数值。在系统级别是不可见，只在指定的会话有效。

3、对象级别的参数：定义为对象的属性，可以影响其作用域内的SQL语句的执行。

V$SYSTEM_PARAMETER视图是Oracle系统视图，查看系统参数以及当前会话的参数的值。由于它可以显示instance级别及session级别的参数，因此也可以用来查看未知属性的当前值。

使用方法：
建议使用SELECT * FROM v$system_parameter语句来查看所有有效参数，我们可以组合和添加其他条件来提高查询的有效性，如下所示：

SELECT *
FROM v$system_parameter
WHERE name LIKE ‘%timezone%’ OR name LIKE ‘%nls%’;
— 这样我们就能查看系统timezone和NLS相关参数的值。

另外，V$SYSTEM_PARAMETER视图还可以获取SID和SERIAL#访问会话的参数值，可用于分析会话的表现形式：

SELECT sid, serial#, value
FROM v$system_parameter
WHERE name = ‘sort_area_size’;
— 查看指定会话的sort_area_size参数的值

官方英文解释

V$SYSTEM_PARAMETER displays information about the initialization parameters that are currently in effect for the instance. A new session inherits parameter values from the instance-wide values.

Column	Datatype	Description
`NUM`	`NUMBER`	Parameter number
`NAME`	`VARCHAR2(80)`	Name of the parameter
`TYPE`	`NUMBER`	Parameter type: `1` – Boolean `2` – String `3` – Integer `4` – Parameter file `5` – Reserved `6` – Big integer
`VALUE`	`VARCHAR2(4000)`	Instance-wide parameter value
`DISPLAY_VALUE`	`VARCHAR2(4000)`	Parameter value in a user-friendly format. For example, if the `VALUE` column shows the value `262144` for a big integer parameter, then the `DISPLAY_VALUE` column will show the value `256K`.
`DEFAULT_VALUE`	`VARCHAR2(255)`	The default value for this parameter. This is the value of the parameter if a value is not explicitly specified for the parameter.
`ISDEFAULT`	`VARCHAR2(9)`	Indicates whether the parameter is set to the default value (`TRUE`) or the parameter value was specified in the parameter file (`FALSE`) The database sets the value of the `ISDEFAULT` column to `TRUE` for parameters that are not specified in the init.ora or server parameter file (SPFILE).
`ISSES_MODIFIABLE`	`VARCHAR2(5)`	Indicates whether the parameter can be changed with `ALTER SESSION` (`TRUE`) or not (`FALSE`)
`ISSYS_MODIFIABLE`	`VARCHAR2(9)`	Indicates whether the parameter can be changed with `ALTER SYSTEM` and when the change takes effect: `IMMEDIATE` – Parameter can be changed with `ALTER SYSTEM` regardless of the type of parameter file used to start the instance. The change takes effect immediately. `DEFERRED` – Parameter can be changed with `ALTER SYSTEM` regardless of the type of parameter file used to start the instance. The change takes effect in subsequent sessions. `FALSE` – Parameter cannot be changed with `ALTER SYSTEM` unless a server parameter file was used to start the instance. The change takes effect in subsequent instances.
`ISPDB_MODIFIABLE`	`VARCHAR2(5)`	Indicates whether the parameter can be modified inside a PDB (`TRUE`) or not (`FALSE`). In a non-CDB, the value of this column is `NULL`.
`ISINSTANCE_MODIFIABLE`	`VARCHAR2(5)`	For parameters that can be changed with `ALTER SYSTEM`, indicates whether the value of the parameter can be different for every instance (`TRUE`) or whether the parameter must have the same value for all Real Application Clusters instances (`FALSE`). If the `ISSYS_MODIFIABLE` column is `FALSE`, then this column is always `FALSE`.
`ISMODIFIED`	`VARCHAR2(8)`	Indicates how the parameter was modified. If an `ALTER SYSTEM` was performed, the value will be `MODIFIED`.
`ISADJUSTED`	`VARCHAR2(5)`	Indicates whether Oracle adjusted the input value to a more suitable value (for example, the parameter value should be prime, but the user input a non-prime number, so Oracle adjusted the value to the next prime number)
`ISDEPRECATED`	`VARCHAR2(5)`	Indicates whether the parameter has been deprecated (`TRUE`) or not (`FALSE`)
`ISBASIC`	`VARCHAR2(5)`	Indicates whether the parameter is a basic parameter (`TRUE`) or not (`FALSE`)
`DESCRIPTION`	`VARCHAR2(255)`	Description of the parameter
`UPDATE_COMMENT`	`VARCHAR2(255)`	Comments associated with the most recent update
`HASH`	`NUMBER`	Hash value for the parameter name
`CON_ID`	`NUMBER`	The ID of the container to which the data pertains. Possible values include: `0`: This value is used for rows containing data that pertain to the entire CDB. This value is also used for rows in non-CDBs. `1`: This value is used for rows containing data that pertain to only the root n: Where n is the applicable container ID for the rows containing data

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