SYNOPSIS

my %stats = $poe_kernel->stat_getdata;
printf "Idle = %3.2f\n", 100*$stats{avg_idle_seconds}/$stats{interval};

DESCRIPTION

POE::Resource::Statistics is a mix-in class for POE::Kernel. It provides features for gathering run-time statistics about POE::Kernel and the applications that use it.

Statistics gathering is enabled with the TRACE_STATISTICS constant. There is no run-time performance penalty when tracing is disabled.

Statistics are totaled every 30 seconds, and a rolling average is maintained for the last two minutes. The data may be retrieved at any time with the stat_getdata() method. Statistics will also be displayed on the console shortly before POE::Kernel's run() returns.

The time() function is used to gather statistics over time. If Time::HiRes is available, it will be used automatically. Otherwise time is measured in whole seconds, and the resulting rounding errors will make the statistics much less useful.

Run-time statistics gathering was added to POE 0.28. It is considered highly experimental. Please be advised that the statistics it gathers are quite likely wrong. They may in fact be useless. The reader is invited to investigate and improve the module's methodologies.

Gathered Statistics

stat_getdata() returns a hashref with a small number of accumulated values. For each accumulator, there will be a corresponding field prefixed ``avg_'' which is the rolling average for that accumulator.

blocked

"blocked" contains the number of events (both user and kernel) which were delayed due to a user event running for too long. On conclusion of the program, POE will display the blocked count.

In theory, one can compare "blocked" with "user_events" to determine how much lag is produced by user code. "blocked" should be as low as possible to ensure minimum user-generated event lag.

In practice, "blocked" is often near or above "user_events". Events that are even the slightest bit late count as being ``blocked''. See "blocked_seconds" for a potentially more useful metric.

blocked_seconds

"blocked_seconds" contains the total number of seconds that events waited in the queue beyond their nominal dispatch times. The average ("avg_blocked_seconds") is generally more useful.

idle_seconds

"idle_seconds" is the amount of time that POE spent doing nothing at all. Typically this time is spent waiting for I/O or timers rather than dispatching events.

interval

"interval" is the average interval over which the statistics counters are recorded. This will typically be 30 seconds, but it can be more if long-running user events prevent statistics from being gathered on time. "interval" may also be less for programs that finish in under half a minute.

"avg_interval" may often be lower, as the very last measurement taken before POE::Kernel's run() returns will almost always have an "interval" less than 30 seconds.

total_duration

"total_duration" contains the total time over which the average was calculated. The ``avg_'' accumulators are averaged over a 2-minute interval. "total_duration" may vary from 120 seconds due to the same reasons as described in ``interval''.

user_events

"user_events" contains the number of events that have been dispatched to user code. ``User'' events do not include POE's internal events, although it will include events dispatched on behalf of wheels.

Shortly before POE::Kernel's run() returns, a "user_load" value will be computed showing the average number of user events that have been dispatched per second. A very active web server should have a high "user_load" value. The higher the user load, the more important it is to have small "blocked" and "blocked_seconds" values.

user_seconds

"user_seconds" is the time that was spent handling user events, including those handled by wheels. "user_seconds" + "idle_seconds" should typically add up to "total_duration". Any difference is unaccounted time in POE, and indicates a flaw in the statistics gathering methodology.

AUTHORS & COPYRIGHTS

Contributed by Nick Williams <[email protected]>.

Please see POE for more information about authors and contributors.