Today's post talks about AWS statistics gathering:
Historical data of current value of metrics can be very useful. But AWS also provides the aggregators, sum, max, min and avg.
If the metrics have continuous values and their sum is important, we can maintain a running total by taking the sum every interval. Typically this interval can be set in the call to grab the statistics.
Since the calls are continuous, their return values are also non-overlapping and therefore summation is straightforward.

function addCurrentToCumulative($current, $cumulative){
foreach ( $current as $metric ){

if (array_key_exists($metric['key'], $cumulative) == false){
$cumulative[$metric['key']] = array('key'=>$metric[key], 'value' => 0, 'units' => $metric['count']);
}

if (array_key_exists('cumulate', $metric) && $metric['cumulate']){

if (array_key_exists($metric['key'], $cumulative)){
$cumulative[$metric['key']]['value'] += $metric['sum'];
}else{
$cumulative[$metric['key']]['value'] = $metric['sum'];
}

}else{
$cumulative[$metric['key']]['value'] = $metric['avg'];
}
}
return $cumulative;
}
function saveOrPrintCumulative($cumulative){
print "\n==========================================================\n";
print " Aggregated Metrics\n";
print "==========================================================\n";

foreach($cumulative as $item){
$key = $item['key'];
$value = $item['value'];
$units = $item['units'];
print "Metric -- $key $value $units \n";
}

}

// after every $interval minutes
// cumulate by adding current to total
// update current with grab_stats

$tablename = "Metrics";
$current = array();
$cumulative = addCurrentToCumulative($current, $cumulative);
$current = grab_stats($client, $tablename);
sleep($interval*60); // seconds
$cumulative = addCurrentToCumulative($current, $cumulative);
$current = grab_stats($client, $tablename);
?>

Note the forward moving cumulation ensures that there are no overlaps or errors introduced.