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MDL-42882 upgrade: improved SQL query

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Kudos to Tim Hunt who came up with this, on mysql with 4 milion
records (and a fast SSD) the performance difference is:

Original: 36.83 sec
New query: 8.63 sec
This commit is contained in:
Dan Poltawski 2014-02-03 12:42:35 +08:00
parent 5f38edeefd
commit b7f4097043
1 changed files with 7 additions and 10 deletions
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17
lib/upgradelib.php
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@ -2096,16 +2096,13 @@ function upgrade_fix_missing_root_folders() {
global $DB, $USER; global $DB, $USER;
$transaction = $DB->start_delegated_transaction(); $transaction = $DB->start_delegated_transaction();
$sql = "SELECT distinct f1.contextid, f1.component, f1.filearea, f1.itemid
FROM {files} f1 left JOIN {files} f2 $sql = "SELECT contextid, component, filearea, itemid
ON f1.contextid = f2.contextid FROM {files}
AND f1.component = f2.component WHERE (component <> 'user' OR filearea <> 'draft')
AND f1.filearea = f2.filearea GROUP BY contextid, component, filearea, itemid
AND f1.itemid = f2.itemid HAVING MAX(CASE WHEN filename = '.' AND filepath = '/' THEN 1 ELSE 0 END) = 0";
AND f2.filename = '.'
AND f2.filepath = '/'
WHERE (f1.component <> 'user' or f1.filearea <> 'draft')
and f2.id is null";
$rs = $DB->get_recordset_sql($sql); $rs = $DB->get_recordset_sql($sql);
$defaults = array('filepath' => '/', $defaults = array('filepath' => '/',
'filename' => '.', 'filename' => '.',