Reduce page deletion lock contention

Bug: T98706
Change-Id: Ib37e74c4737de9d705af28ac2eac06e716dd5f10

diff --git a/includes/page/WikiPage.php b/includes/page/WikiPage.php
index 5e4438a..7d990d9 100644 (file)
--- a/includes/page/WikiPage.php
+++ b/includes/page/WikiPage.php
@@ -2769,9 +2769,16 @@ class WikiPage implements Page, IDBAccessObject {
                $dbw->begin( __METHOD__ );
 
                if ( $id == 0 ) {
-                       $this->loadPageData( 'forupdate' );
+                       // T98706: lock the page from various other updates but avoid using
+                       // WikiPage::READ_LOCKING as that will carry over the FOR UPDATE to
+                       // the revisions queries (which also JOIN on user). Only lock the page
+                       // row and CAS check on page_latest to see if the trx snapshot matches.
+                       $latest = $this->lock();
+
+                       $this->loadPageData( WikiPage::READ_LATEST );
                        $id = $this->getID();
-                       if ( $id == 0 ) {
+                       if ( $id == 0 || $this->getLatest() != $latest ) {
+                               // Page not there or trx snapshot is stale
                                $dbw->rollback( __METHOD__ );
                                $status->error( 'cannotdelete', wfEscapeWikiText( $this->getTitle()->getPrefixedText() ) );
                                return $status;
@@ -2878,6 +2885,24 @@ class WikiPage implements Page, IDBAccessObject {
                return $status;
        }
 
+       /**
+        * Lock the page row for this title and return page_latest (or 0)
+        *
+        * @return integer
+        */
+       protected function lock() {
+               return (int)wfGetDB( DB_MASTER )->selectField(
+                       'page',
+                       'page_latest',
+                       array(
+                               'page_namespace' => $this->getTitle()->getNamespace(),
+                               'page_title' => $this->getTitle()->getDBkey()
+                       ),
+                       __METHOD__,
+                       array( 'FOR UPDATE' )
+               );
+       }
+
        /**
         * Do some database updates after deletion
         *