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PhabricatorFactsUpdateIterator.php
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Sun, Aug 25, 12:14

PhabricatorFactsUpdateIterator.php
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<?php
/*
* Copyright 2012 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* Iterate over objects by update time in a stable way. This iterator only works
* for "normal" Lisk objects: objects with an autoincrement ID and a
* dateModified column.
*/
final class PhabricatorFactsUpdateIterator extends PhutilBufferedIterator {
private $cursor;
private $object;
private $start;
private $ignoreUpdatesDuration = 15;
public function __construct(LiskDAO $object, $start = null) {
if ($start === null) {
$start = '0:0';
}
$this->object = $object;
$this->start = $start;
}
protected function didRewind() {
$this->cursor = $this->start;
}
protected function getCursorFromObject($object) {
return $object->getDateModified().':'.$object->getID();
}
public function key() {
return $this->getCursorFromObject($this->current());
}
protected function loadPage() {
list($after_epoch, $after_id) = explode(':', $this->cursor);
// 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,
$this->getPageSize());
if ($page) {
$this->cursor = $this->getCursorFromObject(end($page));
}
return $page;
}
}

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