NAME¶

pmGetArchiveLabel - fetch the label record from a set of performance metrics archives

C SYNOPSIS¶

#include <pcp/pmapi.h>

int pmGetArchiveLabel(pmLogLabel *lp);

cc ... -lpcp

DESCRIPTION¶

Within the framework of the Performance Co-Pilot (PCP), archives of performance metrics values may be accumulated and saved using the program pmlogger(1) and the LOGIMPORT(3) programming interface.

The routines pmGetArchiveLabel may be used to fetch the label record from a set of archives that has already been opened using pmNewContext(3), or pmDupContext(3), and thereby associated with the current Performance Metrics Application Programming Interface (PMAPI) context.

The result returned via the pointer lp is a structure that must be pre-allocated by the caller and has the following format (defined in pmapi.h).

typedef struct {


  int        magic;       /* PM_LOG_MAGIC | archive format version no. */


  pid_t      pid;         /* PID of logger */


  struct timespec start;  /* start of this archive */


  char       hostname[PM_MAX_HOSTNAMELEN];   /* collection host full name */


  char       timezone[PM_MAX_TIMEZONELEN];   /* generic, squashed $TZ */


  char       zoneinfo[PM_MAX_ZONEINFOLEN];   /* local platform $TZ */
} pmLogLabel;

pmGetArchiveLabel can be used with either version 2 or version 3 archives, however some mapping may be required with the older version 2 archives, e.g. the start time only has microsecond resolution and the zoneinfo field is not present. For detailed information about the archive on-disk format, refer to LOGARCHIVE(5).

For an application using pmGetArchiveLabel, the most useful information from the archive label is likely to be in the fields start, hostname, timezone, and zoneinfo.

The zoneinfo field contains the most detailed timezone information available, and should be used if present (non-zero length string). It will only not be present in the case of version 2 archives - this is a new field added as part of the version 3 format. The timezone field will always be present, however it is the 'squashed' timezone value and in certain situations is not the most accurate timezone.

For older applications using pmGetArchiveLabel, the most useful information from the archive label is likely to be in the fields ll_start, ll_hostname or ll_tz. Note that the size of the ll_hostname field is PM_LOG_MAXHOSTLEN (64 bytes) which is less than MAXHOSTNAMELEN (see gethostbyname(3)) on some platforms. These semantics are necessary to retain backwards compatibility with the PCP archive file format.

pmGetArchiveLabel return zero for success.

COMPATIBILITY¶

Prior to PCP 7.0 and libpcp.so.4 the pmLogLabel structure was somewhat different. To support PMAPI transition, the old interface and semantics can be used if applications are linked with libpcp.so.3 or recompiled with -DPMAPI_VERSION=2.

For a time in PCP 6.x there was a routine with the same semantics as the current pmGetArchiveLabel called pmGetHighResArchiveLabel and a structure with same definition as pmLogLabel called pmHighResLogLabel although these are now deprecated and compile-time support for pmGetHighResArchiveLabel and pmHighResLogLabel will be removed in a future release.

DIAGNOSTICS¶

PM_ERR_NOCONTEXT

the current PMAPI context is either invalid, or not associated with a set of archives

PCP ENVIRONMENT¶

Environment variables with the prefix PCP_ are used to parameterize the file and directory names used by PCP. On each installation, the file /etc/pcp.conf contains the local values for these variables. The $PCP_CONF variable may be used to specify an alternative configuration file, as described in pcp.conf(5). Values for these variables may be obtained programmatically using the pmGetConfig(3) function.

SEE ALSO¶

pmlogger(1), LOGIMPORT(3), PMAPI(3), pmDupContext(3), pmGetConfig(3), pmNewContext(3), LOGARCHIVE(5), pcp.conf(5) and pcp.env(5).