Sybase Device I/O Test
This test monitors the I/O activity on each device on the Sybase server, and proactively alerts administrators to contention for device I/O semaphores. To ensure that this test runs smoothly, enable the enable monitoring configuration parameter on the Sybase server.
Target of the test : A Sybase ASE server on which the MDA tables have been installed
Agent deploying the test : An internal agent
Outputs of the test : One set of results for every Sybase ASE server being monitored.
Parameter | Description |
---|---|
Test Period |
How often should the test be executed. |
Host |
Refers to the IP address of the Sybase server. |
Port |
The port number at which the Sybase server listens to. |
User |
A Sybase user who has the “sa_role”. |
Password |
The password corresponding to the above user. |
Confirm Password |
Confirm the password by retyping it here. |
Measurement | Description | Measurement Unit | Interpretation |
---|---|---|---|
Reads |
The number of reads that occurred on the device during the last measurement period. |
Number |
|
APF reads |
Indicates the number of APF reads that occurred on this device during the last measurement period. |
Number |
Asynchronous prefetch (APF) issues I/O requests for pages before the query needs them so that most pages are in cache by the time query processing needs to access the page. High APF activity can hence improve performance for:
|
Writes |
Indicates the number of writes that occurred on this device during the last measurement period. |
Number |
|
Request |
The number of requests from this device during the last measurement period. |
Number |
|
IO waits |
The number of I/O requests to this device that were waiting during the last measurement period. |
Number |
|
Total io time |
The time taken to read from or write to this device during the last measurement period. |
Msecs |
A high value of this measure indicates that the device is taking too much time to process I/O requests. This could be owing to any of the following reasons:
|
Percentage io granted |
The percentage of IO granted. |
Percent |
Ideally, this value should be high. When Adaptive Server needs to perform a disk I/O, it gives the task to the semaphore for that device in order to acquire a block I/O structure. On SMP systems, multiple engines can try to post I/Os to the same device simultaneously. This creates contention for that semaphore, especially if there are hot devices or if the data is not well distributed across devices. A low value for this measure indicates that many I/O requests were waiting for the semaphore – in other words, it indicates a contention for the semaphore. One solution might be to redistribute the data on the physical devices. |