PMDISCOVERSETUP(3) Library Functions Manual PMDISCOVERSETUP(3)

pmDiscoverSetup, pmDiscoverSetSlots, pmDiscoverSetEventLoop, pmDiscoverSetConfiguration, pmDiscoverSetMetricRegistry, pmDiscoverClose - asynchronous archive location and contents discovery services

#include <pcp/pmwebapi.h>


int pmDiscoverSetup(pmDiscoverModule *module, pmDiscoverCallBacks *callbacks, void *arg);

int pmDiscoverSetSlots(pmDiscoverModule *module, void *slots);
int pmDiscoverSetEventLoop(pmDiscoverModule *module, void *uvloop);
int pmDiscoverSetConfiguration(pmDiscoverModule *module, struct dict *config);
int pmDiscoverSetMetricRegistry(pmDiscoverModule *module, struct mmv_registry *registry);

int pmDiscoverClose(pmDiscoverModule *module);


cc ... -lpcp_web

The pmDiscoverSetup and related functions are an integral part of the libpcp_web API library, as used by and described in pmwebapi(3), pmproxy(1), pmseries(1) and elsewhere. These functions provide an asynchronous event driven mechanism to automatically discover PCP archives created by pmlogger(1) and any other application capable of writing PCP archives. This includes pmrep(1) and other applications using the LOGIMPORT(3) API for importing performance data into the PCP infrastructure and writing PCP archives.

The pmDiscover API services dynamically discover, monitor and manage directories of PCP archives as they are created, written to, compressed and eventually deleted. The underlying archive life-cycle is normally managed by the PCP archive management infrastructure (see pmlogger_daily(1)). Discovered archives that are active (currently being written) are "log-tailed" to extract near live/real-time performance data which is then passed off via registered callbacks for further processing, e.g. to add the data to a redis-server(1) instance. Archives that are compressed or inactive are tracked/monitored but not log-tailed - this is because compressed archives never grow and so log-tailing would never discover any new data. See the --load option in pmseries(1) for a supported mechanism for ingesting previously collected (inctive) PCP archives, whether compressed or not, into a redis-server(1) instance.

The pmDiscover routines can be configured to automatically discover and monitor PCP archives in one or more directories as specified in the pmDiscoverModule, which is initially set up by calling pmDiscoverSetConfiguration to create a module of type pmDiscoverModule, as described above. The resulting module is then passed to pmDiscoverSetup along with an initialized structure of callbacks of type pmDiscoverCallBacks.

Setting up a discovery module and callbacks would normally declare an instance of pmDiscoverSettings, e.g.

#include <pcp/pmwebapi.h>
static pmDiscoverSettings someapp_discover = {
    .callbacks.on_source        = pmSomeappDiscoverSource,
    .callbacks.on_closed        = pmSomeappDiscoverClosed,
    .callbacks.on_labels        = pmSomeappDiscoverLabels,
    .callbacks.on_metric        = pmSomeappDiscoverMetric,
    .callbacks.on_values        = pmSomeappDiscoverValues,
    .callbacks.on_indom         = pmSomeappDiscoverInDom,
    .callbacks.on_text          = pmSomeappDiscoverText,
    .module.on_info             = someapp_logging_function,
};

And then initialize this with API calls similar to the following:

pmDiscoverSetEventLoop(&someapp_discover.module, myevents);
pmDiscoverSetConfiguration(&someapp_discover.module, myconfig);
pmDiscoverSetMetricRegistry(&someapp_discover.module, metric_registry);
pmDiscoverSetup(&someapp_discover.module, &someapp_discover.callbacks, &privatedata);

The above code must then implement each of the declared callbacks etc. to do whatever is required with the data passed in to the callback. Prototypes for these callbacks can be found in the pmwebapi.h header. The callbacks will be made asynchronously, as archives are discovered or deleted and as new data is written to active archive volume and metadata files.

In the case of pmproxy(1), callbacks are registered to capture performance data, which is then sent to redis-server(1) as the database back-end for fast scalable time-series queries by clients of the PMWEBAPI(3) REST API services. Such clients include the pmseries(1) application and pmproxy(1), which is the back-end REST API server for grafana-pcp, a native grafana-server(1) data-source for PCP.

Generally zero on success, or on error a negative return code, see pmerr(1).

The default archive directory is $PCP_ARCHIVE_DIR, which is normally /var/log/pcp/pmlogger. The API recursively descends all sub-directories and also dynamically discovers any new directories or archives found therein.

grafana-server(1), pmerr(1), pmlogger(1), pmproxy(1), pmseries(1), PMWEBAPI(3), mmv_stats_registry(3), PMAPI(3), pmErrStr(3), pcp.conf(5) and pcp.env(5).

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