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<?php |
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namespace MatthiasMullie\Scrapbook\Scale; |
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use MatthiasMullie\Scrapbook\KeyValueStore; |
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use SplObjectStorage; |
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/** |
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* This class lets you scale your cache cluster by sharding the data across |
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* multiple cache servers. |
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* |
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* Pass the individual KeyValueStore objects that compose the cache server pool |
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* into this constructor how you want the data to be sharded. The cache data |
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* will be sharded over them according to the order they were in when they were |
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* passed into this constructor (so make sure to always keep the order the same) |
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* |
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* The sharding is spread evenly and all cache servers will roughly receive the |
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* same amount of cache keys. If some servers are bigger than others, you can |
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* offset this by adding the KeyValueStore object more than once. |
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* |
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* Data can even be sharded among different adapters: one server in the shard |
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* pool can be Redis while another can be Memcached. Not sure why you would even |
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* want that, but you could! |
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* |
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* @author Matthias Mullie <[email protected]> |
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* @copyright Copyright (c) 2014, Matthias Mullie. All rights reserved |
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* @license LICENSE MIT |
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*/ |
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class Shard implements KeyValueStore |
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{ |
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/** |
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* @var KeyValueStore[] |
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*/ |
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protected $caches = array(); |
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/** |
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* Overloadable with multiple KeyValueStore objects. |
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*/ |
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public function __construct(KeyValueStore $cache1, KeyValueStore $cache2 = null /* , [KeyValueStore $cache3, [...]] */) |
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{ |
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$caches = func_get_args(); |
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$caches = array_filter($caches); |
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$this->caches = $caches; |
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} |
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public function addCache(KeyValueStore $cache) |
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{ |
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$this->caches[] = $cache; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function get($key, &$token = null) |
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{ |
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return $this->getShard($key)->get($key, $token); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function getMulti(array $keys, array &$tokens = null) |
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{ |
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$shards = $this->getShards($keys); |
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$results = array(); |
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$tokens = array(); |
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/** @var KeyValueStore $shard */ |
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foreach ($shards as $shard) { |
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$keysOnShard = $shards[$shard]; |
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$results += $shard->getMulti($keysOnShard, $shardTokens); |
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$tokens += $shardTokens ?: array(); |
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} |
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return $results; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function set($key, $value, $expire = 0) |
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{ |
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return $this->getShard($key)->set($key, $value, $expire); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function setMulti(array $items, $expire = 0) |
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{ |
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$shards = $this->getShards(array_keys($items)); |
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$results = array(); |
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/** @var KeyValueStore $shard */ |
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foreach ($shards as $shard) { |
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$keysOnShard = $shards[$shard]; |
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$itemsOnShard = array_intersect_key($items, array_flip($keysOnShard)); |
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$results += $shard->setMulti($itemsOnShard, $expire); |
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} |
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return $results; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function delete($key) |
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{ |
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return $this->getShard($key)->delete($key); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function deleteMulti(array $keys) |
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{ |
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$shards = $this->getShards($keys); |
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$results = array(); |
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/** @var KeyValueStore $shard */ |
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foreach ($shards as $shard) { |
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$keysOnShard = $shards[$shard]; |
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$results += $shard->deleteMulti($keysOnShard); |
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} |
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return $results; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function add($key, $value, $expire = 0) |
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{ |
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return $this->getShard($key)->add($key, $value, $expire); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function replace($key, $value, $expire = 0) |
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{ |
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return $this->getShard($key)->replace($key, $value, $expire); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function cas($token, $key, $value, $expire = 0) |
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{ |
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return $this->getShard($key)->cas($token, $key, $value, $expire); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function increment($key, $offset = 1, $initial = 0, $expire = 0) |
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{ |
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return $this->getShard($key)->increment($key, $offset, $initial, $expire); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function decrement($key, $offset = 1, $initial = 0, $expire = 0) |
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{ |
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return $this->getShard($key)->decrement($key, $offset, $initial, $expire); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function touch($key, $expire) |
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{ |
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return $this->getShard($key)->touch($key, $expire); |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function flush() |
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{ |
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$result = true; |
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foreach ($this->caches as $cache) { |
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$result &= $cache->flush(); |
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} |
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return (bool) $result; |
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} |
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/** |
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* {@inheritdoc} |
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*/ |
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public function getCollection($name) |
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{ |
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$shard = new static($this->caches[0]->getCollection($name)); |
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$count = count($this->caches); |
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for ($i = 1; $i < $count; ++$i) { |
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$shard->addCache($this->caches[$i]->getCollection($name)); |
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} |
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return $shard; |
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} |
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/** |
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* Get the shard (KeyValueStore object) that corresponds to a particular |
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* cache key. |
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* |
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* @param string $key |
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* |
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* @return KeyValueStore |
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*/ |
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protected function getShard($key) |
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{ |
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/* |
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* The hash is so we can deterministically randomize the spread of keys |
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* over servers: if we were to just spread them based on key name, we |
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* may end up with a large chunk of similarly prefixed keys on the same |
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* server. Hashing the key will ensure similar looking keys can still |
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* result in very different values, yet they result will be the same |
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* every time it's repeated for the same key. |
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* Since we don't use the hash for encryption, the fastest algorithm |
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* will do just fine here. |
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*/ |
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$hash = crc32($key); |
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// crc32 on 32-bit machines can produce a negative int |
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$hash = abs($hash); |
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$index = $hash % count($this->caches); |
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return $this->caches[$index]; |
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} |
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/** |
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* Get a [KeyValueStore => array of cache keys] map (SplObjectStorage) for |
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* multiple cache keys. |
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* |
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* @return \SplObjectStorage |
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*/ |
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protected function getShards(array $keys) |
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{ |
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$shards = new \SplObjectStorage(); |
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foreach ($keys as $key) { |
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$shard = $this->getShard($key); |
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if (!isset($shards[$shard])) { |
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$shards[$shard] = array(); |
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} |
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$shards[$shard] = array_merge($shards[$shard], array($key)); |
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} |
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return $shards; |
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} |
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} |
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