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MDL-67363 task: Add adhoc task quality of service balancing

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Brendan Heywood
2019-12-03 12:21:10 +11:00
parent 800563e415
commit 4971da0bfa
2 changed files with 237 additions and 0 deletions
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lib/classes/task/manager.php
+71
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@@ -471,6 +471,75 @@ class manager {
return $tasks;
}
/**
* Ensure quality of service for the ad hoc task queue.
*
* This reshuffles the adhoc tasks queue to balance by type to ensure a
* level of quality of service per type, while still maintaining the
* relative order of tasks queued by timestamp.
*
* @param array $records array of task records
* @return void
*/
public static function ensure_adhoc_task_qos(array $records): array {
$count = count($records);
if ($count == 0) {
return $records;
}
$queues = []; // This holds a queue for each type of adhoc task.
$limits = []; // The relative limits of each type of task.
$limittotal = 0;
// Split the single queue up into queues per type.
foreach ($records as $record) {
$type = $record->classname;
if (!array_key_exists($type, $queues)) {
$queues[$type] = [];
}
if (!array_key_exists($type, $limits)) {
$limits[$type] = 1;
$limittotal += 1;
}
$queues[$type][] = $record;
}
$qos = []; // Our new queue with ensured quality of service.
$seed = $count % $limittotal; // Which task queue to shuffle from first?
do {
$shuffled = 0;
// Now cycle through task type queues and interleaving the tasks
// back into a single queue.
foreach ($limits as $type => $limit) {
// Just interleaving the queue is not enough, because after
// any task is processed the whole queue is rebuilt again. So
// we need to deterministically start on different types of
// tasks so that *on average* we rotate through each type of task.
//
// We achieve this by using a $seed to start moving tasks off a
// different queue each time. The seed is based on the task count
// modulo the number of types of tasks on the queue. As we count
// down this naturally cycles through each type of record.
if ($seed < 1) {
$shuffled = 1;
$seed += 1;
continue;
}
$task = array_splice($queues[$type], 0, 1);
$qos = array_merge($qos, $task);
// Stop if we didn't move any tasks onto the main queue.
$shuffled += count($task);
}
} while ($shuffled > 0);
return $qos;
}
/**
* This function will dispatch the next adhoc task in the queue. The task will be handed out
* with an open lock - possibly on the entire cron process. Make sure you call either
@@ -491,6 +560,8 @@ class manager {
$params = array('timestart1' => $timestart);
$records = $DB->get_records_select('task_adhoc', $where, $params);
$records = self::ensure_adhoc_task_qos($records);
foreach ($records as $record) {
if ($lock = $cronlockfactory->get_lock('adhoc_' . $record->id, 0)) {