L-electron-Rare/moodle
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

MDL-40893 backup: cache question answers for performance

Browse Source 
To constrain memory we only cache a single question's answers.
A quiz must display this many answers, so it will not result
in undue memory pressure.

We now match on the full answer text rather than the first 255
characters.  This removes the risk of matching questions with the
same start.
This commit is contained in:
Russell Smith
2013-08-16 10:06:59 +10:00
parent 14e8af6687
commit 5821a7c5f1
1 changed files with 24 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files
backup/moodle2/restore_qtype_plugin.class.php
+24 -18
View File
@@ -35,6 +35,18 @@ defined('MOODLE_INTERNAL') || die();
*/
abstract class restore_qtype_plugin extends restore_plugin {
/*
* A simple answer to id cache for a single questions answers.
* @var array
*/
private $questionanswercache = array();
/*
* The id of the current question in the questionanswercache.
* @var int
*/
private $questionanswercacheid = null;
/**
* Add to $paths the restore_path_elements needed
* to handle question_answers for a given question
@@ -147,38 +159,32 @@ abstract class restore_qtype_plugin extends restore_plugin {
// The question existed, we need to map the existing question_answers
} else {
// Look in question_answers by answertext matching
$sql = 'SELECT id
FROM {question_answers}
WHERE question = ?
AND ' . $DB->sql_compare_text('answer', 255) . ' = ' . $DB->sql_compare_text('?', 255);
$params = array($newquestionid, $data->answertext);
$newitemid = $DB->get_field_sql($sql, $params);
// Not able to find the answer, let's try cleaning the answertext
// of all the question answers in DB as slower fallback. MDL-30018.
if (!$newitemid) {
// Have we cached the current question?
if ($this->questionanswercacheid !== $newquestionid) {
// The question changed, purge and start again!
$this->questionanswercache = array();
$params = array('question' => $newquestionid);
$answers = $DB->get_records('question_answers', $params, '', 'id, answer');
$this->questionanswercacheid = $newquestionid;
// Cache all cleaned answers for a simple text match.
foreach ($answers as $answer) {
// Clean in the same way than {@link xml_writer::xml_safe_utf8()}.
// MDL-30018: Clean in the same way as {@link xml_writer::xml_safe_utf8()}.
$clean = preg_replace('/[\x-\x8\xb-\xc\xe-\x1f\x7f]/is','', $answer->answer); // Clean CTRL chars.
$clean = preg_replace("/\r\n|\r/", "\n", $clean); // Normalize line ending.
if ($clean === $data->answertext) {
$newitemid = $data->id;
}
$this->questionanswercache[$clean] = $answer->id;
}
}
// If we haven't found the newitemid, something has gone really wrong, question in DB
// is missing answers, exception
if (!$newitemid) {
if (!isset($this->questionanswercache[$data->answertext])) {
// If we haven't found the matching answer, something has gone really wrong, the question in the DB
// is missing answers, throw an exception.
$info = new stdClass();
$info->filequestionid = $oldquestionid;
$info->dbquestionid = $newquestionid;
$info->answer = $data->answertext;
throw new restore_step_exception('error_question_answers_missing_in_db', $info);
}
$newitemid = $this->questionanswercache[$data->answertext];
}
// Create mapping (we'll use this intensively when restoring question_states. And also answerfeedback files)
$this->set_mapping('question_answer', $oldid, $newitemid);