установить параметры времени сбора для текущего контекста PMAPI (set collection time parameters for the current PMAPI context)
Имя (Name)
pmSetMode - set collection time parameters for the current PMAPI
context
Синопсис C (C Synopsis)
#include <pcp/pmapi.h>
int pmSetMode(int mode, const struct timeval *when, int delta);
cc ... -lpcp
Описание (Description)
pmSetMode is used to define the collection time and/or mode for
accessing performance metrics and meta-data in the current
Performance Metrics Application Programming Interface (PMAPI)
context. This mode affects the semantics of subsequent calls to
the following PMAPI routines: pmFetch(3), pmFetchArchive(3),
pmLookupDesc(3), pmGetInDom(3), pmLookupInDom(3) and
pmNameInDom(3).
If mode is PM_MODE_LIVE then all information is returned from the
active pool of performance metrics as of the time that the PMAPI
call is made, and the other two parameters to pmSetMode are
ignored. PM_MODE_LIVE is the default mode when a new PMAPI
context of type PM_CONTEXT_HOST is created.
If the mode is not PM_MODE_LIVE, then the when parameter defines
a time origin, and all requests for meta-data (metric
descriptions and instance identifiers from the instance domains)
will be processed to reflect the state of the meta-data as of the
time origin, i.e. we use the last state of this information at,
or before, the time origin.
If the mode is PM_MODE_INTERP then, in the case of pmFetch(3),
the underlying code will use an interpolation scheme to compute
the values of the metrics from the values recorded for times in
the proximity of the time origin. A mode of PM_MODE_INTERP may
only be used with an archive context.
If the mode is PM_MODE_FORW then, in the case of pmFetch(3), the
collection of recorded metric values will be scanned in a
forwards direction in time, until values for at least one of the
requested metrics is located after the time origin, and then all
requested metrics stored in the set of archives at that time will
be returned with the corresponding timestamp. A mode of
PM_MODE_FORW may only be used with an archive context.
If the mode is PM_MODE_BACK then, the situation is the same as
for PM_MODE_FORW, except a pmFetch(3) will be serviced by
scanning the collection of recorded metrics in a backwards
direction in time for metrics before the time origin. A mode of
PM_MODE_BACK may only be used with an archive context.
If the mode is PM_MODE_FORW or PM_MODE_BACK, and no qualifying
metrics can be found in the requested direction of searching
before the end or start of the set of archive logs is found, then
pmFetch(3) returns the special error indicator, PM_ERR_EOL.
For modes other than PM_MODE_LIVE, after each successful
pmFetch(3), the time origin is reset to the timestamp returned
via the pmResult structure from pmFetch(3).
The pmSetMode parameter delta defines an additional number of
time units that should be used to adjust the time origin
(forwards or backwards), after the new time origin from the
pmResult has been determined. This automatic adjustment of the
time origin only occurs when the mode is PM_MODE_INTERP, and the
adjustment is applied, even if the pmFetch(3) fails because the
time origin is outside the range defined by the records in a set
of archive logs, i.e. returns PM_ERR_EOL.
By default delta is interpreted as milliseconds (but see the
LARGE DELTA VALUES section below).
Using these mode options, an application can implement replay,
playback, fast forward, reverse, etc. for performance metric
values held in the set of archive logs by alternating calls to
pmSetMode and pmFetch(3).
As a special case, if when is NULL then the mode and delta
arguments are used as described above, but the current time in
the archive is not altered.
Примеры (Examples)
The following code fragment may be used to dump just those values
recorded in an archive in correct temporal sequence, for a
selected set of performance metrics; this uses the default
collection time mechanisms.
pmNewContext(PM_CONTEXT_ARCHIVE, "myarchive");
while (pmFetch(npmid, pmidlist, &result) != PM_ERR_EOL) {
/*
* process real metric values as of result->timestamp
*/
. . .
pmFreeResult(result);
}
Alternatively, to replay interpolated metrics from the log in
reverse chronological order, at 10 second intervals (of recorded
time), the following code fragment could be used.
struct timeval mytime;
mytime.tv_sec = 0x7fffffff; /* or use pmGetArchiveEnd(&mtime) */
pmSetMode(PM_MODE_BACK, &mytime, 0);
pmFetchArchive(&result);
mytime = result->timestamp;
pmFreeResult(result);
pmSetMode(PM_MODE_INTERP | PM_XTB_SET(PM_TIME_SEC), &mytime, -10);
while (pmFetch(numpmid, pmidlist, &result) != PM_ERR_EOL) {
/*
* process interpolated metric values as of
* result->timestamp
*/
. . .
pmFreeResult(result);
}
LARGE DELTA VALUES
Because delta is an int and treated as milliseconds by default
there is a limit on the maximum absolute value of delta that can
be specified with this default interpretation, namely about 24
days if a signed int has 31 bits of precision. To accommodate
longer values of delta the high-order bits of the mode parameter
is also used to optionally set the units of time for the delta
parameter. To specify the units of time use the PM_XTB_SET macro
with one of the values PM_TIME_NSEC, PM_TIME_MSEC, PM_TIME_SEC,
etc. to set the mode as follows:
PM_MODE_INTERP | PM_XTB_SET(PM_TIME_XXXX)
The following code shows how this could be done if the desired
delta is initially encoded in interval (a struct timeval).
struct timeval interval;
int mode;
mode = ...
if (abs(interval.tv_sec / (3600*24)) <= 24) {
/* default encoding of milliseconds is fine */
mode = PM_MODE_INTERP;
delta = interval.tv_sec * 1000 + (interval.tv_usec + 500)/ 1000;
}
else {
/* encode delta in units of seconds */
mode = PM_MODE_INTERP | PM_XTB_SET(PM_TIME_SEC);
delta = interval.tv_sec + (interval.tv_usec + 500000)/ 1000000;
}
For millisecond encoding of delta, using PM_XTB_SET(PM_TIME_MSEC)
is functionally equivalent to not using PM_XTB_SET at all.
Диагностика (Diagnostic)
PM_ERR_MODE
The mode parameter is invalid
Смотри также (See also)
PMAPI(3), pmFetch(3), pmFetchArchive(3), pmGetInDom(3),
pmLookupDesc(3), pmLookupInDom(3) and pmNameInDom(3).
