Buffer Busy Waits 
Definition
This submonitor in the SAP/Oracle Database Monitor lets you check buffer busy waits in the Oracle database.
A buffer busy wait indicates that there are some buffers in the buffer cache that multiple processes are attempting to access concurrently. This event happens because one of the following is true:
· An Oracle block is being read into the buffer cache by another session and the session is waiting for that read to complete.
· The buffer is already in the buffer cache but in an incompatible mode (that is, some other session is changing the buffer)
Use
You choose Detailed Analyses ® Overall activity ® Buffer Busy Waits.
You can view history information in this monitor.
Structure
Entries marked “RAC only” appear only for Oracle Real Application Cluster (RAC).
- Buffer Busy Waits
This tab page contains information on buffer busy waits:
Column |
Description |
Inst Id RAC only |
Database instance ID |
Class |
Class of block |
Ttl waits |
Total number of waits due to this class of block |
Tm Wait (ms) |
Total of all wait
times for all waits due to this |
Avg Tm wait (ms) |
Average duration of wait due to this class of block in milliseconds |
%BBW/Inst |
Percentage of waits due to this class of block for each instance |
% of Time of BBW/Inst |
Percentage of time spent waiting due to this class of block for each instance |
%BBW |
Percentage of waits due to this class of block for all instances |
% of Time of BBW |
Percentage of time spent waiting due to this class of block for all instances |
In single-instance – that is, non-RAC – environments, the following is true:
· %BBW/Inst shows the same value as %BBW
· % of Time of BBW/Instshows the same value as % of Time of BBW
· RAC only: Buffer Busy Waits with Total Lines
This tab page shows the same information as in the table above plus Total lines for each Class of buffer busy wait. This helps you identify a buffer cache contention problem that is not caused by a specific instance.