pmTrimNameSpace - prune a performance metrics name space

#include <pcp/pmapi.h>

int pmTrimNameSpace(void);

cc ... -lpcp

In some (rare) cases it is helpful to prune the Performance Metrics Name Space (PMNS) to match the available metrics.

The default PMNS that is accessible to a Performance Metrics Application Programming Interface (PMAPI) client is provided by the current PMAPI context:

  • for a PMAPI context of type PM_CONTEXT_HOST the PMNS is provided by pmcd(1) on the associated host and no pruning is required
  • for a PMAPI context of type PM_CONTEXT_ARCHIVE the PMNS is stored within the associated Performance Co-Pilot (PCP) archive and no pruning is required
  • for a PMAPI context of type PM_CONTEXT_LOCAL at the first PMAPI call requiring access to the PMNS it is loaded from the default local location $PCP_VAR_DIR/pmns/root (or $PMNS_DEFAULT) and no pruning is required.

If the default PMNS is in effect then calling pmTrimNameSpace is a no-op and returns zero with no change to the PMNS.

PMAPI clients also have the option of over-riding the default PMNS by loading a local PMNS from a file (see PMNS(5) for the format) by calling pmLoadASCIINameSpace(3) or pmLoadNameSpace(3) and this is when some PMNS pruning may be useful.

If a local PMNS is in effect when pmTrimNameSpace is called then the first action is to restore the PMNS to the state as of the completion of the last pmLoadASCIINameSpace(3) or pmLoadNameSpace(3), so that the effects of consecutive calls to pmTrimNameSpace are not additive.

The subsequent actions of pmTrimNameSpace depend on the type of the current PMAPI context.

  • For a context of type PM_CONTEXT_ARCHIVE the local PMNS is trimmed to exclude metrics for which no description can be found in the PCP archive. The PMNS is further trimmed to remove empty subtrees that do not contain any performance metric. Since PCP archives usually contain some subset of all metrics named in a PMNS, pmTrimNameSpace effectively prunes the application's PMNS to contain only the names of the metrics in the archive.
  • For a context of type PM_CONTEXT_HOST or PM_CONTEXT_LOCAL no further action is required.

On success, pmTrimNameSpace returns zero.

there has been some earlier problem with establishing the relevant PMNS
the current PMAPI context is invalid

pmlogger(1), PMAPI(3), pmLoadASCIINameSpace(3), pmLoadNameSpace(3), pmNewContext(3) and PMNS(5).

PCP Performance Co-Pilot