From fdf9d73bb1435076a5cd8a3652991d0e6fb434f9 Mon Sep 17 00:00:00 2001
From: Domas Mituzas <midom@users.mediawiki.org>
Date: Sat, 7 Apr 2007 07:35:54 +0000
Subject: [PATCH] - add simple row estimation mechanism, allows preparing heavy
 queries better :) - use estimates instead of select count(*) for jobs in
 Special:Statistics, won't scan million-row-tables too often

---
 includes/Database.php          | 31 +++++++++++++++++++++++++++++++
 includes/SpecialStatistics.php |  2 +-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/includes/Database.php b/includes/Database.php
index 9af91352cc..6b7014f758 100644
--- a/includes/Database.php
+++ b/includes/Database.php
@@ -1124,6 +1124,10 @@ class Database {
 			$sql = $this->limitResult($sql, $options['LIMIT'],
 				isset($options['OFFSET']) ? $options['OFFSET'] : false);
 		$sql = "$sql $postLimitTail";
+		
+		if (isset($options['EXPLAIN'])) {
+			$sql = 'EXPLAIN ' . $sql;
+		}
 
 		return $this->query( $sql, $fname );
 	}
@@ -1156,6 +1160,33 @@ class Database {
 		return $obj;
 
 	}
+	
+	/**
+	 * Estimate rows in dataset
+	 * Returns estimated count, based on EXPLAIN output
+	 * Takes same arguments as Database::select()
+	 */
+	
+	function estimateRowCount( $table, $vars='*', $conds='', $fname = 'Database::estimateRowCount', $options = array() ) {
+		$options['EXPLAIN']=true;
+		$res = $this->select ($table, $vars, $conds, $fname, $options );
+		if ( $res === false )
+			return false;
+		if (!$this->numRows($res)) {
+			$this->freeResult($res);
+			return 0;
+		}
+		
+		$rows=1;
+	
+		while( $plan = $this->fetchObject( $res ) ) {
+			$rows *= ($plan->rows > 0)?$plan->rows:1; // avoid resetting to zero
+		}
+		
+		$this->freeResult($res);
+		return $rows;		
+	}
+	
 
 	/**
 	 * Removes most variables from an SQL query and replaces them with X or N for numbers.
diff --git a/includes/SpecialStatistics.php b/includes/SpecialStatistics.php
index 59cca3ed77..1c9e0ab61c 100644
--- a/includes/SpecialStatistics.php
+++ b/includes/SpecialStatistics.php
@@ -23,7 +23,7 @@ function wfSpecialStatistics() {
 	$users = SiteStats::users();
 
 	$admins = $dbr->selectField( 'user_groups', 'COUNT(*)', array( 'ug_group' => 'sysop' ), $fname );
-	$numJobs = $dbr->selectField( 'job', 'COUNT(*)', '', $fname );
+	$numJobs = $dbr->estimateRowCount('job');
 
 	if ($action == 'raw') {
 		$wgOut->disable();
-- 
2.20.1