The memory-part can easily be handled by MemoryStore. There's just 1 gotcha:
when an item is to be deleted (but not yet committed), it needs to be deleted
from the MemoryStore too, but we need to be able to make a distinction
between "this is deleted" and "this value is not known in this memory cache,
fall back to real cache".
This is where this class comes in to play: we'll add an additional "expired"
method, which allows BufferedStore to just expire the keys that are supposed
to be deleted (instead of deleting them) - then we can keep track of when
a key is just not known, or known-but-deleted (=expired)
/**
* In addition to all writes being stored to $local, we'll also
* keep get() values around ;).
*
* {@inheritdoc}
*/
public function getMulti(array $keys, array &$tokens = null)
{
$values = $this->transaction->getMulti($keys, $tokens);
$missing = array_diff_key($values, $this->local->getMulti($keys));
if (!empty($missing)) {
$this->local->setMulti($missing);
}
return $values;
}
/**
* {@inheritdoc}
*/
public function flush()
{
$success = $this->local->flush();
if ($success === false) {
return false;
}
// clear all buffered writes, flush wipes them out anyway
$this->clear();
// make sure that reads, from now on until commit, don't read from cache
$this->suspend = true;
$this->defer->flush();
return true;
}