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<?php |
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namespace Disque\Connection\Node; |
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use InvalidArgumentException; |
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/** |
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* A prioritizer switching nodes if they have more jobs by a given margin |
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* |
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* This class prioritizes nodes by job count and its Disque priority. Because |
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* there is a cost to switch, it doesn't switch from the current node unless |
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* the new candidate has a safe margin over the current node. |
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* |
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* This margin can be set manually and defaults to 5%, ie. the new candidate |
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* must have 5% more jobs than the current node. |
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* |
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* This parameter makes the prioritizer behave conservatively - it prefers |
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* the status quo and won't switch immediately if the difference is small. |
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* |
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* You can make the prioritizer eager by setting the margin to 0, or more |
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* conservative by setting it higher. Setting the margin to negative values |
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* is not allowed. |
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*/ |
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class ConservativeJobCountPrioritizer implements NodePrioritizerInterface |
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{ |
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/** |
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* @var float A margin to switch from the current node |
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* |
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* 0.05 means the new node must have 5% more jobs than the current node |
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* in order to recommend switching over. |
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*/ |
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private $marginToSwitch = 0.05; |
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/** |
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* Get the margin to switch |
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* |
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* @return float |
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*/ |
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public function getMarginToSwitch() |
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{ |
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return $this->marginToSwitch; |
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} |
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/** |
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* Set the margin to switch |
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* |
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* @param float $marginToSwitch A positive float or 0 |
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* |
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* @throws InvalidArgumentException |
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*/ |
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public function setMarginToSwitch($marginToSwitch) |
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{ |
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if ($marginToSwitch < 0) { |
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throw new InvalidArgumentException('Margin to switch must not be negative'); |
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} |
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$this->marginToSwitch = $marginToSwitch; |
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} |
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/** |
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* @inheritdoc |
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*/ |
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public function sort(array $nodes, $currentNodeId) |
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{ |
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// Optimize for a "cluster" consisting of just 1 node - skip everything |
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if (count($nodes) === 1) { |
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return $nodes; |
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} |
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uasort($nodes, function(Node $nodeA, Node $nodeB) use ($currentNodeId) { |
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$priorityA = $this->calculateNodePriority($nodeA, $currentNodeId); |
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$priorityB = $this->calculateNodePriority($nodeB, $currentNodeId); |
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if ($priorityA === $priorityB) { |
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return 0; |
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} |
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// Nodes with a higher priority should go first |
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return ($priorityA < $priorityB) ? 1 : -1; |
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}); |
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return $nodes; |
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} |
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/** |
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* Calculate the node priority from its job count, stick to the current node |
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* |
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* As the priority is based on the number of jobs, higher is better. |
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* |
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* @param Node $node |
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* @param string $currentNodeId |
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* |
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* @return float Node priority |
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*/ |
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private function calculateNodePriority(Node $node, $currentNodeId) |
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{ |
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$priority = $node->getJobCount(); |
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if ($node->getId() === $currentNodeId) { |
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$margin = 1 + $this->marginToSwitch; |
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$priority = $priority * $margin; |
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} |
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// Apply a weight determined by the node priority as assigned by Disque. |
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// Priority 1 means the node is healthy. |
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// Priority 10 to 100 means the node is probably failing, or has failed |
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$disquePriority = $node->getPriority(); |
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// Disque node priority should never be lower than 1, but let's be sure |
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if ($disquePriority < Node::PRIORITY_OK) { |
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$disquePriorityWeight = 1; |
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} elseif (Node::PRIORITY_OK <= $disquePriority && $disquePriority < Node::PRIORITY_POSSIBLE_FAILURE) { |
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// Node is OK, but Disque may have assigned a lower priority to it |
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// We use the base-10 logarithm in the formula, so priorities |
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// 1 to 10 transform into a weight of 1 to 0.5. When Disque starts |
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// using more priority steps, priority 9 will discount about a half |
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// of the job count. |
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$disquePriorityWeight = 1 / (1 + log10($disquePriority)); |
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} else { |
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// Node is failing, or it has failed |
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$disquePriorityWeight = 0; |
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} |
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$priority = $priority * $disquePriorityWeight; |
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return (float) $priority; |
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} |
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} |
mariano /
disque-php
