From fe029f8777ccb7d7138b5cf6238b8857b6598996 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Fri, 15 Aug 2014 10:52:20 -0700
Subject: [PATCH] Added DatabaseBase::selectRowCount() method

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

Change-Id: If1cfc52ea22fd09d34915c29b45d0b487d28d15a
---
 includes/db/Database.php                  | 36 +++++++++++++++++++++--
 includes/specials/SpecialMergeHistory.php |  4 +--
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/includes/db/Database.php b/includes/db/Database.php
index 9584e466f1..9b783a99d6 100644
--- 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 492eb3b5b1..3c9b515086 100644
--- 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' );
 
-- 
2.20.1