MDL-24355 Greatly improved performance of the tag correlation function and fixed up bugs with it
This commit is contained in:
Sam Hemelryk
+89
-44
@@ -758,59 +758,104 @@ function tag_cleanup() {
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* It works as a cache for a potentially heavy load query done at the 'tag_instance' table.
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* So, the 'tag_correlation' table stores redundant information derived from the 'tag_instance' table.
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*
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* @param number $min_correlation cutoff percentage (optional, default is 2)
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* @param number $mincorrelation cutoff percentage (optional, default is 2)
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*/
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function tag_compute_correlations($min_correlation=2) {
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function tag_compute_correlations($mincorrelation = 2) {
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global $CFG;
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if (!$all_tags = get_records_list('tag')) {
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return;
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}
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$mincorrelation = (int)$mincorrelation;
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// This mighty one line query fetches a row from the database for every
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// individual tag correlation. We then need to process the rows collecting
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// the correlations for each tag id.
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// The fields used by this query are as follows:
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// tagid : This is the tag id, there should be at least $mincorrelation
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// rows for each tag id.
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// correlation : This is the tag id that correlates to the above tagid field.
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// correlationid : This is the id of the row in the tag_correlation table that
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// relates to the tagid field and will be NULL if there are no
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// existing correlations
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$sql = "SELECT pairs.tagid, pairs.correlation, pairs.ocurrences, co.id AS correlationid
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FROM (
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SELECT ta.tagid, tb.tagid AS correlation, COUNT(*) AS ocurrences
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FROM {$CFG->prefix}tag_instance ta
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JOIN {$CFG->prefix}tag_instance tb ON (ta.itemtype = tb.itemtype AND ta.itemid = tb.itemid AND ta.tagid <> tb.tagid)
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GROUP BY ta.tagid, tb.tagid
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HAVING COUNT(*) > $mincorrelation
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) pairs
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LEFT JOIN {$CFG->prefix}tag_correlation co ON co.tagid = pairs.tagid
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ORDER BY pairs.tagid ASC, pairs.ocurrences DESC, pairs.correlation ASC";
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$rs = get_recordset_sql($sql);
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$tag_correlation_obj = new object();
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foreach($all_tags as $tag) {
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// Set up an empty tag correlation object
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$tagcorrelation = new stdClass;
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$tagcorrelation->id = null;
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$tagcorrelation->tagid = null;
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$tagcorrelation->correlatedtags = array();
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// query that counts how many times any tag appears together in items
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// with the tag passed as argument ($tag_id)
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$query = "SELECT tb.tagid ".
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"FROM {$CFG->prefix}tag_instance ta INNER JOIN {$CFG->prefix}tag_instance tb ON ta.itemid = tb.itemid ".
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"WHERE ta.tagid = {$tag->id} AND tb.tagid != {$tag->id} ".
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"GROUP BY tb.tagid ".
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"HAVING COUNT(*) > $min_correlation ".
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"ORDER BY COUNT(*) DESC";
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// We store each correction id in this array so we can remove any correlations
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// that no longer exist.
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$correlations = array();
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$correlated = array();
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// Correlated tags happen when they appear together in more occasions
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// than $min_correlation.
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if ($tag_correlations = get_records_sql($query)) {
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foreach($tag_correlations as $correlation) {
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// commented out - now done in query. kept here in case it breaks on some db
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// if($correlation->nr >= $min_correlation){
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$correlated[] = $correlation->tagid;
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// }
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// Iterate each row of the result set and build them into tag correlations.
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while ($row = rs_fetch_next_record($rs)) {
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if ($row->tagid != $tagcorrelation->tagid) {
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// The tag id has changed so its now time to process the tag
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// correlation information we have.
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$tagcorrelationid = tag_process_computed_correlation($tagcorrelation);
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if ($tagcorrelationid) {
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$correlations[] = $tagcorrelationid;
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}
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// Now we reset the tag correlation object so we can reuse it and set it
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// up for the current record.
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$tagcorrelation = new stdClass;
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$tagcorrelation->id = $row->correlationid;
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$tagcorrelation->tagid = $row->tagid;
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$tagcorrelation->correlatedtags = array();
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}
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if (empty($correlated)) {
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continue;
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}
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$correlated = implode(',', $correlated);
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//var_dump($correlated);
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//saves correlation info in the caching table
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if ($tag_correlation_obj = get_record('tag_correlation', 'tagid', $tag->id, '', '', '', '', 'id')) {
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$tag_correlation_obj->correlatedtags = $correlated;
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update_record('tag_correlation', $tag_correlation_obj);
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} else {
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$tag_correlation_obj = new stdClass();
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$tag_correlation_obj->tagid = $tag->id;
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$tag_correlation_obj->correlatedtags = $correlated;
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insert_record('tag_correlation', $tag_correlation_obj);
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}
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$tagcorrelation->correlatedtags[] = $row->correlation;
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}
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// Update the current correlation after the last record.
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$tagcorrelationid = tag_process_computed_correlation($tagcorrelation);
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if ($tagcorrelationid) {
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$correlations[] = $tagcorrelationid;
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}
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// Close the recordset
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rs_close($rs);
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// Remove any correlations that weren't just identified
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delete_records_select('tag_correlation', 'id NOT IN ('.join(',', $correlations).')');
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}
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/**
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* This function processes a tag correlation and makes changes in the database
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* as required.
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*
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* The tag correlation object needs have both a tagid property and a correlatedtags
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* property that is an array.
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*
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* @param stdClass $tagcorrelation
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* @return int The id of the tag correlation that was just processed.
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*/
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function tag_process_computed_correlation(stdClass $tagcorrelation) {
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// You must provide a tagid and correlatedtags must be set and be an array
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if (empty($tagcorrelation->tagid) || !isset($tagcorrelation->correlatedtags) || !is_array($tagcorrelation->correlatedtags)) {
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return false;
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}
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// The row tagid doesn't match the current tag id which means we are onto
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// the next tag. Before we switch over we need to either insert or update
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// the correlation.
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$tagcorrelation->correlatedtags = join(',', $tagcorrelation->correlatedtags);
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if (!empty($tagcorrelation->id)) {
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// The tag correlation already exists so update it
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update_record('tag_correlation', $tagcorrelation);
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} else {
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// This is a new correlation to insert
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$tagcorrelation->id = insert_record('tag_correlation', $tagcorrelation, true);
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}
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return $tagcorrelation->id;
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}
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/**
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