Oracle flashback buffer is allocated in the shared pool.

In Oracle 10 Gb, if the flashback function is enabled for the relevant database, the Oracle database allocates the Oracle flashback buffer in the shared pool. The following is part of the Oracle database startup log, we can clearly see that flashback buffer is allocated 3981204 bytes in the shared pool.

Reference

 
 

  
  
Wed Dec 30 15:20:40 2009  
  
  
Allocated 3981204 bytes in shared pool for flashback generation buffer  
  
  
Starting background process RVWR  
  
  
RVWR started with pid=16, OS id=724 
 
 

You can also see the size of the Oracle flashback buffer in the data dictionary:

Reference

 
 

  
  
SQL> select name,bytes from V$sgastat  
  
  
2 where pool=’shared pool’  
  
  
3 and name like ‘%flash%’;  
  
  
NAME BYTES  
  
  
flashback generation buff 3981204  
 
 

When the flashback buffer space is insufficient, the flashback buf free by RVWR wait event may occur. Oracle does not provide parameters to adjust the flashback buffer. For high throughput, the initial size of the concurrency system does not meet the system requirements.

Currently, the log_buffer size in the system is 7012352 bytes. Change it to 10 MB, restart the database, and observe the changes in the Oracle flashback buffer.

Reference

 
 

  
  
SQL> show parameter log_buffer  
  
  
NAME TYPE VALUE  
  
  
log_buffer integer 7012352  
  
  
SQL> alter system set log_buffer=10000000 scope=spfile;  
  
  
System altered.  
  
  
SQL> select name,bytes from V$sgastat  
  
  
2 where pool=’shared pool’  
  
  
3 and name like ‘%flash%’;  
  
  
NAME BYTES  
  
  
flashback generation buff 3981204  
  
  
SQL> startup force  
  
  
ORACLE instance started.  
  
  
Total System Global Area 536870912 bytes  
  
  
Fixed Size 1262764 bytes  
  
  
Variable Size 155192148 bytes  
  
  
Database Buffers 369098752 bytes  
  
  
Redo Buffers 11317248 bytes  
  
  
Database mounted.  
  
  
Database opened.  
  
  
SQL> select name,bytes from V$sgastat  
  
  
2 where pool=’shared pool’  
  
  
3 and name like ‘%flash%’;  
  
  
NAME BYTES  
  
  
flashback generation buff 3981204  
 
 

We can see that the flashback generation buff size has not changed.

Further, observe the hidden parameters related to flashback. The above content is an introduction to the Oracle flashback buffer parameter research. I hope you will find some gains.