Added DatabaseBase::selectRowCount() method

* Useful for doing COUNT(*) with a LIMIT for performance
* Made MergeHistory use it

Change-Id: If1cfc52ea22fd09d34915c29b45d0b487d28d15a

diff --git a/includes/db/Database.php b/includes/db/Database.php
index 9584e46..9b783a9 100644 (file)
--- a/includes/db/Database.php
+++ b/includes/db/Database.php
@@ -1752,7 +1752,7 @@ abstract class DatabaseBase implements IDatabase, DatabaseType {
        }
 
        /**
-        * Estimate rows in dataset.
+        * Estimate the number of rows in dataset
         *
         * MySQL allows you to estimate the number of rows that would be returned
         * by a SELECT query, using EXPLAIN SELECT. The estimate is provided using
@@ -1771,8 +1771,8 @@ abstract class DatabaseBase implements IDatabase, DatabaseType {
         * @param array $options Options for select
         * @return int Row count
         */
-       public function estimateRowCount( $table, $vars = '*', $conds = '',
-               $fname = __METHOD__, $options = array()
+       public function estimateRowCount(
+               $table, $vars = '*', $conds = '', $fname = __METHOD__, $options = array()
        ) {
                $rows = 0;
                $res = $this->select( $table, array( 'rowcount' => 'COUNT(*)' ), $conds, $fname, $options );
@@ -1785,6 +1785,36 @@ abstract class DatabaseBase implements IDatabase, DatabaseType {
                return $rows;
        }
 
+       /**
+        * Get the number of rows in dataset
+        *
+        * This is useful when trying to do COUNT(*) but with a LIMIT for performance.
+        *
+        * Takes the same arguments as DatabaseBase::select().
+        *
+        * @param string $table Table name
+        * @param string $vars Unused
+        * @param array|string $conds Filters on the table
+        * @param string $fname Function name for profiling
+        * @param array $options Options for select
+        * @return int Row count
+        * @since 1.24
+        */
+       public function selectRowCount(
+               $table, $vars = '*', $conds = '', $fname = __METHOD__, $options = array()
+       ) {
+               $rows = 0;
+               $sql = $this->selectSQLText( $table, '1', $conds, $fname, $options );
+               $res = $this->query( "SELECT COUNT(*) AS rowcount FROM ($sql) tmp_count" );
+
+               if ( $res ) {
+                       $row = $this->fetchRow( $res );
+                       $rows = ( isset( $row['rowcount'] ) ) ? $row['rowcount'] : 0;
+               }
+
+               return $rows;
+       }
+
        /**
         * Removes most variables from an SQL query and replaces them with X or N for numbers.
         * It's only slightly flawed. Don't use for anything important.

diff --git a/includes/specials/SpecialMergeHistory.php b/includes/specials/SpecialMergeHistory.php
index 492eb3b..3c9b515 100644 (file)
--- a/includes/specials/SpecialMergeHistory.php
+++ b/includes/specials/SpecialMergeHistory.php
@@ -388,11 +388,11 @@ class SpecialMergeHistory extends SpecialPage {
                }
                # Check that there are not too many revisions to move
                $limit = 5000; // avoid too much slave lag
-               $count = $dbw->select( 'revision', '1',
+               $count = $dbw->selectRowCount( 'revision', '1',
                        array( 'rev_page' => $this->mTargetID, $timewhere ),
                        __METHOD__,
                        array( 'LIMIT' => $limit + 1 )
-               )->numRows();
+               );
                if ( $count > $limit ) {
                        $this->getOutput()->addWikiMsg( 'mergehistory-fail-toobig' );