Buffer Cache Page
In order to avoid excessive disk I/O within databases, Oracle uses a buffer cache, a portion of the SGA that holds copies of data blocks read from data files. All user processes concurrently connected to the instance share access to the database buffer cache.
To open the Buffer Cache page
- Select the Spotlight on Oracle connection in the Spotlight Browser.
-
Click Configuration & Memory | Buffer Cache.
Pools Grid
This grid specifies all the buffer pools that the cache contains — pools such as the DEFAULT, KEEP, and RECYCLE pools. Each pool in the buffer cache uses a different strategy to control the way its data blocks age out of the cache.
Note: Select / Highlight a pool. The Buffer Cache Details grid displays details of the objects within that pool.
| Column | Description |
|---|---|
|
Pool name |
The name of the buffer pool. |
|
Blocks |
How many blocks in the pool. |
|
Block size |
The size of blocks in the pool. |
|
DB block gets |
The number of times a current block was requested. |
|
Consistent gets |
The number of times a consistent read was requested. |
|
Physical reads |
The number of data blocks read from disk. |
|
Hit ratio |
100 * ((DB block gets + Consistent gets) - Physical reads)) / (DB block gets + Consistent gets) |
Note: DB block gets, Consistent gets and Physical reads are obtained from Oracle's v$buffer_pool_statistics view.
Buffer Cache Details Grid
Buffer Cache Details contains information on the objects in the pool selected from the Pools Grid.
| Column | Description |
|---|---|
|
Object name |
The name of the object in the specified pool. |
|
Total Segment Blocks |
The object has this number of segment blocks. Blocks are either in the buffer cache or not in the buffer cache. |
|
Blocks In Buffers |
The number of segment blocks in the buffer cache. |
|
Blocks not in Buffers |
A high number of blocks not in the buffer cache for an object with a high number of physical reads could have a performance impact. |
|
Physical Reads |
By default the grid is ordered by the highest number of physical reads. |