As a consequence of network, host or Performance Metrics Collector
Daemon (PMCD) failures, an application'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 system 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 reconnect 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 thereafter.
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 pmRegisterDerived(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
When attempting to connect to a remote pmcd(1) on a machine that is
booting, pmReconnectContext could potentially 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.
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
firstname.lastname@example.org. This page was obtained from the project's upstream
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Performance Co-Pilot PCP PMRECONNECTCONTEXT(3)