Merge "Change Title::getPreviousRevisionID (and next) to ignore PRIMARY"

diff --combined includes/Title.php
index a5bb9c6,1ddb2fc..e45994c
--- 1/includes/Title.php
--- 2/includes/Title.php
+++ b/includes/Title.php
@@@ -2943,6 -2943,8 +2943,6 @@@ class Title implements LinkTarget 
                                        continue;
                                }
  
 -                              // This code should be refactored, now that it's being used more generally,
 -                              // But I don't really see any harm in leaving it in Block for now -werdna
                                $expiry = $dbr->decodeExpiry( $row->pr_expiry );
  
                                // Only apply the restrictions if they haven't expired!
@@@ -3961,14 -3963,22 +3961,22 @@@
         * @return int|bool Old revision ID, or false if none exists
         */
        public function getPreviousRevisionID( $revId, $flags = 0 ) {
-               $db = ( $flags & self::GAID_FOR_UPDATE ) ? wfGetDB( DB_MASTER ) : wfGetDB( DB_REPLICA );
+               /* This function and getNextRevisionID have bad performance when
+                  used on a page with many revisions on mysql. An explicit extended
+                  primary key may help in some cases, if the PRIMARY KEY is banned:
+                  T159319 */
+               if ( $flags & self::GAID_FOR_UPDATE ) {
+                       $db = wfGetDB( DB_MASTER );
+               } else {
+                       $db = wfGetDB( DB_REPLICA, 'contributions' );
+               }
                $revId = $db->selectField( 'revision', 'rev_id',
                        [
                                'rev_page' => $this->getArticleID( $flags ),
                                'rev_id < ' . intval( $revId )
                        ],
                        __METHOD__,
-                       [ 'ORDER BY' => 'rev_id DESC' ]
+                       [ 'ORDER BY' => 'rev_id DESC', 'IGNORE INDEX' => 'PRIMARY' ]
                );
  
                if ( $revId === false ) {
@@@ -3986,14 -3996,18 +3994,18 @@@
         * @return int|bool Next revision ID, or false if none exists
         */
        public function getNextRevisionID( $revId, $flags = 0 ) {
-               $db = ( $flags & self::GAID_FOR_UPDATE ) ? wfGetDB( DB_MASTER ) : wfGetDB( DB_REPLICA );
+               if ( $flags & self::GAID_FOR_UPDATE ) {
+                       $db = wfGetDB( DB_MASTER );
+               } else {
+                       $db = wfGetDB( DB_REPLICA, 'contributions' );
+               }
                $revId = $db->selectField( 'revision', 'rev_id',
                        [
                                'rev_page' => $this->getArticleID( $flags ),
                                'rev_id > ' . intval( $revId )
                        ],
                        __METHOD__,
-                       [ 'ORDER BY' => 'rev_id' ]
+                       [ 'ORDER BY' => 'rev_id', 'IGNORE INDEX' => 'PRIMARY' ]
                );
  
                if ( $revId === false ) {