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feature #35362 [Cache] Add LRU + max-lifetime capabilities to ArrayCa…

…che (nicolas-grekas)

This PR was merged into the 5.1-dev branch.

Discussion
----------

[Cache] Add LRU + max-lifetime capabilities to ArrayCache

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | Fix https://github.com/orgs/symfony/projects/1#card-30686676
| License       | MIT
| Doc PR        | -

In #32294 (comment), @andrerom writes:

> if you plan to expose use of ArrayAdapter to a wider audience you should probably also add the following features to it:
> - max item limit to avoid reaching memory limits
> - own (very low, like default 100-500ms) TTL for in-memory caching, as it's in practice stale data when used in concurrent scenarios
>
> If you want to be advance you can also:
>
> - keep track of use, and evict cache items based on that using LFU when reaching limit
> - in-memory cache is domain & project specific in terms of how long it's somewhat "safe" to keep items in memory, so either describe when to use and not use on a per pool term, or allow use of pool to pass in flags to opt out of in-memory cache for cases developer knows it should be ignored

This PR implements these suggestions, via two new constructor arguments: `$maxLifetime` and `$maxItems`.

In Yaml:
```yaml
services:
    app.lru150_cache:
        parent: cache.adapter.array
        arguments:
            $maxItems: 150
            $maxLifetime: 0.150

framework:
    cache:
        pools:
            my_chained_pool:
                adapters:
                  - app.lru150_cache
                  - cache.adapter.filesystem
```

This configuration adds a local memory cache that keeps max 150 elements for 150ms on top of a filesystem cache.

/cc @lyrixx since you were also interested in it.

Commits
-------

48a5d5e [Cache] Add LRU + max-lifetime capabilities to ArrayCache
  • Loading branch information
nicolas-grekas committed Jan 27, 2020
2 parents 5182135 + 48a5d5e commit b22a58449c3b994ef57275ddd51bc1fa6fa11d7d
@@ -15,10 +15,15 @@
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerAwareTrait;
use Symfony\Component\Cache\CacheItem;
use Symfony\Component\Cache\Exception\InvalidArgumentException;
use Symfony\Component\Cache\ResettableInterface;
use Symfony\Contracts\Cache\CacheInterface;

/**
* An in-memory cache storage.
*
* Acts as a least-recently-used (LRU) storage when configured with a maximum number of items.
*
* @author Nicolas Grekas <p@tchwork.com>
*/
class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInterface, ResettableInterface
@@ -29,13 +34,25 @@ class ArrayAdapter implements AdapterInterface, CacheInterface, LoggerAwareInter
private $values = [];
private $expiries = [];
private $createCacheItem;
private $maxLifetime;
private $maxItems;

/**
* @param bool $storeSerialized Disabling serialization can lead to cache corruptions when storing mutable values but increases performance otherwise
*/
public function __construct(int $defaultLifetime = 0, bool $storeSerialized = true)
public function __construct(int $defaultLifetime = 0, bool $storeSerialized = true, int $maxLifetime = 0, int $maxItems = 0)
{
if (0 > $maxLifetime) {
throw new InvalidArgumentException(sprintf('Argument $maxLifetime must be a positive integer, %d passed.', $maxLifetime));
}

if (0 > $maxItems) {
throw new InvalidArgumentException(sprintf('Argument $maxItems must be a positive integer, %d passed.', $maxItems));
}

$this->storeSerialized = $storeSerialized;
$this->maxLifetime = $maxLifetime;
$this->maxItems = $maxItems;
$this->createCacheItem = \Closure::bind(
static function ($key, $value, $isHit) use ($defaultLifetime) {
$item = new CacheItem();
@@ -84,6 +101,13 @@ public function delete(string $key): bool
public function hasItem($key)
{
if (\is_string($key) && isset($this->expiries[$key]) && $this->expiries[$key] > microtime(true)) {
if ($this->maxItems) {
// Move the item last in the storage
$value = $this->values[$key];
unset($this->values[$key]);
$this->values[$key] = $value;
}

return true;
}
CacheItem::validateKey($key);
@@ -97,7 +121,12 @@ public function hasItem($key)
public function getItem($key)
{
if (!$isHit = $this->hasItem($key)) {
$this->values[$key] = $value = null;
$value = null;

if (!$this->maxItems) {
// Track misses in non-LRU mode only
$this->values[$key] = null;
}
} else {
$value = $this->storeSerialized ? $this->unfreeze($key, $isHit) : $this->values[$key];
}
@@ -164,7 +193,9 @@ public function save(CacheItemInterface $item)
$value = $item["\0*\0value"];
$expiry = $item["\0*\0expiry"];

if (null !== $expiry && $expiry <= microtime(true)) {
$now = microtime(true);

if (null !== $expiry && $expiry <= $now) {
$this->deleteItem($key);

return true;
@@ -173,7 +204,23 @@ public function save(CacheItemInterface $item)
return false;
}
if (null === $expiry && 0 < $item["\0*\0defaultLifetime"]) {
$expiry = microtime(true) + $item["\0*\0defaultLifetime"];
$expiry = $item["\0*\0defaultLifetime"];
$expiry = $now + ($expiry > ($this->maxLifetime ?: $expiry) ? $this->maxLifetime : $expiry);
} elseif ($this->maxLifetime && (null === $expiry || $expiry > $now + $this->maxLifetime)) {
$expiry = $now + $this->maxLifetime;
}

if ($this->maxItems) {
unset($this->values[$key]);

// Iterate items and vacuum expired ones while we are at it
foreach ($this->values as $k => $v) {
if ($this->expiries[$k] > $now && \count($this->values) < $this->maxItems) {
break;
}

unset($this->values[$k], $this->expiries[$k]);
}
}

$this->values[$key] = $value;
@@ -210,15 +257,21 @@ public function commit()
public function clear(string $prefix = '')
{
if ('' !== $prefix) {
$now = microtime(true);

foreach ($this->values as $key => $value) {
if (0 === strpos($key, $prefix)) {
if (!isset($this->expiries[$key]) || $this->expiries[$key] <= $now || 0 === strpos($key, $prefix)) {
unset($this->values[$key], $this->expiries[$key]);
}
}
} else {
$this->values = $this->expiries = [];

if ($this->values) {
return true;
}
}

$this->values = $this->expiries = [];

return true;
}

@@ -258,8 +311,20 @@ private function generateItems(array $keys, $now, $f)
{
foreach ($keys as $i => $key) {
if (!$isHit = isset($this->expiries[$key]) && ($this->expiries[$key] > $now || !$this->deleteItem($key))) {
$this->values[$key] = $value = null;
$value = null;

if (!$this->maxItems) {
// Track misses in non-LRU mode only
$this->values[$key] = null;
}
} else {
if ($this->maxItems) {
// Move the item last in the storage
$value = $this->values[$key];
unset($this->values[$key]);
$this->values[$key] = $value;
}

$value = $this->storeSerialized ? $this->unfreeze($key, $isHit) : $this->values[$key];
}
unset($keys[$i]);
@@ -314,8 +379,12 @@ private function unfreeze(string $key, bool &$isHit)
$value = false;
}
if (false === $value) {
$this->values[$key] = $value = null;
$value = null;
$isHit = false;

if (!$this->maxItems) {
$this->values[$key] = null;
}
}
}

@@ -1,6 +1,11 @@
CHANGELOG
=========

5.1.0
-----

* added max-items + LRU + max-lifetime capabilities to `ArrayCache`

5.0.0
-----

@@ -55,4 +55,36 @@ public function testGetValuesHitAndMiss()
$this->assertArrayHasKey('bar', $values);
$this->assertNull($values['bar']);
}

public function testMaxLifetime()
{
$cache = new ArrayAdapter(0, false, 1);

$item = $cache->getItem('foo');
$item->expiresAfter(2);
$cache->save($item->set(123));

$this->assertTrue($cache->hasItem('foo'));
sleep(1);
$this->assertFalse($cache->hasItem('foo'));
}

public function testMaxItems()
{
$cache = new ArrayAdapter(0, false, 0, 2);

$cache->save($cache->getItem('foo'));
$cache->save($cache->getItem('bar'));
$cache->save($cache->getItem('buz'));

$this->assertFalse($cache->hasItem('foo'));
$this->assertTrue($cache->hasItem('bar'));
$this->assertTrue($cache->hasItem('buz'));

$cache->save($cache->getItem('foo'));

$this->assertFalse($cache->hasItem('bar'));
$this->assertTrue($cache->hasItem('buz'));
$this->assertTrue($cache->hasItem('foo'));
}
}

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