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Guidelines | |
Consistent Changes per Consistent Gets (ConsChgRatio)
The ConsChgRatio parameter reports consistent changes as a percentage of consistent gets. A consistent change occurs each time that an action is required by the Oracle instance to bring a block subject to a consistent get back to its target read consistency point.
These operations require navigation of rollback segment entry chains and can be highly consumptive of both CPU and disk I/O. Also, these operations may require the allocation of an extra block buffer in which to store the read consistent version of the block.
This parameter uses the following formula:
prf_consistent_changes |
prf_consistent_gets |
This is the percentage of consistent gets that are consistent changes, or in other words, or a block was modified but not committed. Another user issued a read on that block and must see the original data, so this user issues a consistent get. If the original data is still in memory, we are done. If not, Oracle must bring back the data and this act is called a consistent change.
Recommendations
Consider enabling multi-block writes.
A large ConsChgRatio implies either there are a lot of long running transactions or there aren't enough DB_BLOCK_BUFFERS.
Thresholds for alarms and warnings
Item | Default threshold | State |
|---|---|---|
Border range | 0-0 | OK |
Alarm1 range | 5-100 | WARN |
Alarm2 range | 0-0 | OK |
BMC PATROL properties
Attribute | Default value |
|---|---|
Application class | ORACLE_PERFORMANCE |
Command type | Not applicable |
Platform | All |
Icon style | Graph |
Unit | Percentage of consistent gets |
Border range | Undefined |
Alarm1 range | 5-100 WARN |
Alarm2 range | Undefined |
Scheduling(poll time) | Poll time of collector |
Active at installation | Yes |
Parameter type | Consumer |
Value set by | CollPerformance |
BMC ProactiveNet Performance Management properties
Property | Default value |
|---|---|
Monitor type | Oracle Database Performance |
Key Performance Indicator | No |
Monitor for abnormalities | Yes |
Graph by default | No |
Availability | No |
Response time | No |
Normal distribution | Yes |
Statistical | Yes |