NAME

       pmReconnectContext - reconnect to a PMAPI context

C SYNOPSIS

       #include <pcp/pmapi.h>

       int pmReconnectContext(int handle);

       cc ... -lpcp

DESCRIPTION

       As  a  consequence  of network, host or Performance Metrics Collector Daemon (PMCD) failures, an applica‐
       tion's connection to a PMCD may be established and then subsequently lost.

       The routine pmReconnectContext allows an application to request that the  context  identified  by  handle
       should be re-established, provided the associated metrics source is accessible.

       When the source of metrics associated with the context handle is pmcd(1), then to avoid flooding the sys‐
       tem  with  reconnect requests, pmReconnectContext will only attempt a reconnection after a suitable delay
       from the previous unsuccessful attempt to reconnect this context. This imposed restriction on the  recon‐
       nect  re-try  time interval uses an exponential back-off so that the initial delay is 5 seconds after the
       first unsuccessful attempt, then 10 seconds, then 20 seconds, then 40 seconds and then 80 seconds  there‐
       after.

       The  environment  variable  PMCD_RECONNECT_TIMEOUT  may  be  used to redefine the back-off intervals, see
       PMAPI(3).

       Calling pmReconnectContext with a handle identifying a currently connected pmcd(1) context will cause the
       connection to be broken before any reconnection is attempted.

       If handle identifies a context associated with an archive source of metrics,  pmReconnectContext  returns
       without delay.

       If the reconnection succeeds, pmReconnectContext returns handle.

       As a side-effect of reconnecting, any derived metrics that have previously been defined using pmRegister‐
       Derived(3), pmRegisterDerivedMetric(3) or pmLoadDerivedConfig(3) will be re-processed and re-bound to the
       available  metrics  from  the  reconnected source.  The support of dynamic definition for derived metrics
       provides one use case where pmReconnectContext may be called even if the connection to the metrics source
       has not been lost.

       Note that even in the case of a successful reconnection, pmReconnectContext does not change  the  current
       Performance Metrics Application Programming Interface (PMAPI) context, so handle remains valid.

       When attempting to connect to a remote pmcd(1) on a machine that is booting, pmReconnectContext could po‐
       tentially block for a long time until the remote machine finishes its initialization.  pmReconnectContext
       will  abort  and return an error if the connection has not been established after some specified interval
       has elapsed.  The default interval is 5 seconds.  This may be modified by setting PMCD_CONNECT_TIMEOUT in
       the environment to a real number of seconds for the desired timeout.  This is most useful in cases  where
       the  remote  host is at the end of a slow network, requiring longer latencies to establish the connection
       correctly.

CAVEAT

       Applications that use gethostbyname(3) should exercise caution because the static fields in  struct  hos‐
       tent may not be preserved across some PMAPI(3) calls.  In particular, pmNewContext(3) and pmReconnectCon‐
       text(3) both may call gethostbyname(3) internally.

DIAGNOSTICS

       PM_ERR_NOCONTEXT

              handle does not identify a valid PMAPI context

       -ETIMEDOUT

              The re-try time has not elapsed, or the reconnection is attempted and fails.

ENVIRONMENT

       PMCD_CONNECT_TIMEOUT
              Timeout period (in seconds) for pmcd(1) connection attempts.

       PMCD_RECONNECT_TIMEOUT
              Redefines the back-off intervals - refer to PMAPI(3).

SEE ALSO

       pmcd(1),  PMAPI(3),  pmLoadDerivedConfig(3), pmNewContext(3), pmRegisterDerived(3), pmRegisterDerivedMet‐
       ric(3) and pmUseContext(3).

Performance Co-Pilot                                   PCP                                 PMRECONNECTCONTEXT(3)