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What is a PMDA?

Performance Co-Pilot (PCP) is an open source infrastructure for monitoring, visualizing, recording, responding to, and controlling the status, activity, and performance of networks, computers, applications, and servers.

PCP makes use of add-ons called Performance Metrics Domain Agents (PMDAs) to fetch performance metrics for specific domains, such as specific database servers, specialised hardware, custom applications, etc.

For more information, see the Performance Co-Pilot Programmer's Guide.

What is a PMDA++

PCP includes support for writing PMDAs in C, Perl and Python. PMDA++ is a header-only library that allows developers to write PMDAs in C++. It is just a light C++ wrapper around PCP's C APIs.

Writing a basic PMDA with PMDA++

Note, this section assumes that you are already familiar with basic PMDA concepts. If you have not already done so, you should read the Performance Co-Pilot Programmer's Guide.

TO write a basic PMDA using PMDA++:

1. Create a new class derived from pcp::pmda.

#include <pcp-cpp/pmda.hpp>

class basic_pmda : public pcp::pmda {

}

2. Implement the pure-virtual get_pmda_name and default_pmda_domain_number functions:

#include <pcp-cpp/pmda.hpp>

class basic_pmda : public pcp::pmda {
public:

    virtual std::string get_pmda_name() const
    {
        return "basic";
    }

    virtual int default_pmda_domain_number() const
    {
        return 456;
    }
}

3. Implement the pure-virtual get_supported_metrics function to declare the metrics this PMDA makes available:

    virtual pcp::metrics_description get_supported_metrics() const
    {
        // A single "basic.time" metric, with cluster ID 123 and item ID 456.
        return pcp::metrics_description()(123)
            (456, "time",pcp::type<uint32_t>(), PM_SEM_COUNTER,
             pcp::units(0,1,0, 0,PM_TIME_SEC,0));
    }

4. Implement the pure-virtual fetch_value function to fetch actual metric value(s):

    virtual pmAtomValue fetch_value(const pcp::pmda::metric_id &metric) const
    {
        // Return the current time.
        return pcp::atom(metric.type, time(NULL));
    }

5. Add either a DSO or daemon entry-point function, or both.

// DSO entry point.
extern "C" void basic_init(pmdaInterface *interface)
{
    pcp::pmda::init_dso<basic_pmda>(interface);
}

// Daemon entry point.
int main(int argc, char *argv[])
{
    return pcp::pmda::run_daemon<basic_pmda>(argc, argv);
}

And that's it! There's a lot of other virtual functions that may be overridden to customize / extend the PMDA's behaviour.

See the Reference section below.

See the Reference section below.

See the Reference section below.

For complete examples, take a look at trivial.cpp and simple.cpp.

Reference

Coming soon...