Oracle 参数 SERIAL_REUSE 官方解释，作用，如何配置最优化建议

本站中文解释

=true

**SERIAL_REUSE参数**

SERIAL_REUSE参数是oracle中重要的参数之一，直接影响到oracle的分布式事务处理和应用程序性能。它默认为false，这意味着当事务结束时，如果没有外部的“引用”，oracle会释放事务所在的序列号（比如说，在以前的cursors中会保存序列号），并且重新生成新的序列号来唤醒新的事务。

如果将SERIAL_REUSE参数设置为true，oracle就不会放弃以前的分布式事务中生成的序列号，而是会引用以前的序列号，然后重复使用它们。

正确设置SERIAL_REUSE参数有助于提高数据库的性能，特别是在重复执行相同的分布式事务中。在复杂的分布事务处理系统中，该参数也可以带来精确的并行度和精确的吞吐量，但要确保不影响现有的分布式事务的精确性，所以应该尽量避免将SERIAL_REUSE参数设置为true。

官方英文解释

SERIAL_REUSE specifies which types of cursors make use of the serial-reusable memory feature. This feature allocates private cursor memory in the SGA so that it can be reused (serially, not concurrently) by sessions executing the same cursor.

Note:

The SERIAL_REUSE parameter is deprecated. It is retained for backward compatibility only.

Values

• disable

  Disables the option for all SQL statement types. This value overrides any other values included in the list.

• all

  Enables the option for both DML and SELECT statements. Equivalent to setting select, dml, and plsql.

• select

  Enables the option for SELECT statements.

• dml

  Enables the option for DML statements.

• plsql

  Currently has no effect (although PL/SQL packages do support the serial-reuse memory option using PL/SQL pragmas).

Note:

If CURSOR_SPACE_FOR_TIME is set to true, then the value of SERIAL_REUSE is ignored and treated as if it were set to disable.

See Also:

“CURSOR_SPACE_FOR_TIME”