Displaying the request histogram facility pattern
The rhist p request displays the request histogram facility pattern.
The rhist p request returns the entire enumeration of the request size and latency ranges. The facility must be enabled for a pattern to be returned. If there are no mounted file systems at the time this request is issued, then the request still runs and returns data. The pattern is displayed for both read and write.
Table 1 describes the keywords for the rhist p response, in the order that they appear in the output. These keywords are used only when the mmpmon command is invoked with the -p flag.
| Keyword | Description |
|---|---|
| _n_ | IP address of the node responding. This is the address by which GPFS knows the node. |
| _nn_ | The hostname that corresponds to the IP address (the _n_ value). |
| _req_ | The action requested. In this case, the value is p. |
| _rc_ | Indicates the status of the operation. |
| _t_ | Indicates the current time of day in seconds (absolute seconds since Epoch (1970)). |
| _tu_ | Microseconds part of the current time of day. |
| _k_ | The kind, r or w, (read or write) depending on what the statistics are for. |
| _R_ | Request size range, minimum, and maximum number of bytes. |
| _L_ | Latency range, minimum and maximum, in milliseconds. |
The request size ranges are in bytes. The zero-value used for the higher limit of the last size range means 'and higher'. The request size ranges can be changed by using the rhist nr request.
The latency times are in milliseconds. The zero-value used for the higher limit of the last latency range means 'and higher'. The latency ranges can be changed by using the rhist nr request.
The rhist p request allows an application to query for the entire latency pattern. The application can then configure itself accordingly. Since latency statistics are reported only for ranges with non-zero counts, the statistics responses might be sparse. By querying for the pattern, an application can be certain to learn the complete histogram set. The user may have changed the pattern by using the rhist nr request. For this reason, an application should query for the pattern and analyze it before requesting statistics.
If the facility has never been enabled, then the _rc_ field is non-zero. An _rc_ value of 16 indicates that the histogram operations lock is busy. Retry the request.
If the facility has been previously enabled, then the rhist p request still displays the pattern even when rhist off is currently in effect.
If there are no mounted file systems at the time rhist p is issued, then the pattern is still displayed.