NAME

       pmTrimNameSpace - prune a performance metrics name space

C SYNOPSIS

       #include <pcp/pmapi.h>

       int pmTrimNameSpace(void);

       cc ... -lpcp

DESCRIPTION

       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.

DIAGNOSTICS

       PM_ERR_NOPMNS
              there has been some earlier problem with establishing the relevant PMNS

       PM_ERR_NOCONTEXT
              the current PMAPI context is invalid

SEE ALSO

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