ORA-4031 When Enabling Flashback In 19c

刘泽宇

现象：
After upgrading database to 19c where flashback is enabled and when a guaranteed restore point is created, the following error occurs:

SQL> alter DATABASE FLASHBACK ON;
alter DATABASE FLASHBACK ON
*
ERROR at line 1:
ORA-04031: unable to allocate 15937408 bytes of shared memory ("shared pool","unknown object","sga heap(1,0)","flashback generation buffer")

原因：
This is due to insufficient contiguous space in shared pool required for as flashback buffer.

处理方法：
To avoid future similar errors, set the following parameter and restart the database:   

alter system set "_allocate_flashback_buffer"=TRUE scope=spfile sid='*';

This will pre-allocate flashback buffer during database startup.  Memory will be allocated even if we don't plan to create restore point later.