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PhabricatorFactUpdateIterator.php
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Wed, Jul 17, 07:50

PhabricatorFactUpdateIterator.php
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<?php
/**
* Iterate over objects by update time in a stable way. This iterator only works
* for "normal" Lisk objects: objects with an auto-increment ID and a
* dateModified column.
*/
final class PhabricatorFactUpdateIterator extends PhutilBufferedIterator {
private $cursor;
private $object;
private $position;
private $ignoreUpdatesDuration = 15;
private $set;
public function __construct(LiskDAO $object) {
$this->set = new LiskDAOSet();
$this->object = $object->putInSet($this->set);
}
public function setPosition($position) {
$this->position = $position;
return $this;
}
protected function didRewind() {
$this->cursor = $this->position;
}
protected function getCursorFromObject($object) {
if ($object->hasProperty('dateModified')) {
return $object->getDateModified().':'.$object->getID();
} else {
return $object->getID();
}
}
public function key() {
return $this->getCursorFromObject($this->current());
}
protected function loadPage() {
$this->set->clearSet();
if ($this->object->hasProperty('dateModified')) {
if ($this->cursor) {
list($after_epoch, $after_id) = explode(':', $this->cursor);
} else {
$after_epoch = 0;
$after_id = 0;
}
// NOTE: We ignore recent updates because once we process an update we'll
// never process rows behind it again. We need to read only rows which
// we're sure no new rows will be inserted behind. If we read a row that
// was updated on the current second, another update later on in this
// second could affect an object with a lower ID, and we'd skip that
// update. To avoid this, just ignore any rows which have been updated in
// the last few seconds. This also reduces the amount of work we need to
// do if an object is repeatedly updated; we will just look at the end
// state without processing the intermediate states. Finally, this gives
// us reasonable protections against clock skew between the machine the
// daemon is running on and any machines performing writes.
$page = $this->object->loadAllWhere(
'((dateModified > %d) OR (dateModified = %d AND id > %d))
AND (dateModified < %d - %d)
ORDER BY dateModified ASC, id ASC LIMIT %d',
$after_epoch,
$after_epoch,
$after_id,
time(),
$this->ignoreUpdatesDuration,
$this->getPageSize());
} else {
if ($this->cursor) {
$after_id = $this->cursor;
} else {
$after_id = 0;
}
$page = $this->object->loadAllWhere(
'id > %d ORDER BY id ASC LIMIT %d',
$after_id,
$this->getPageSize());
}
if ($page) {
$this->cursor = $this->getCursorFromObject(end($page));
}
return $page;
}
}

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