From be1f60b6ea1da6f488a3fbde498f011bddd31a39 Mon Sep 17 00:00:00 2001
From: Arlo Breault <abreault@wikimedia.org>
Date: Wed, 16 Oct 2024 21:06:12 -0400
Subject: [PATCH] Force the use of the category index when paging by category

The EXPLAIN in P70205#281191 shows the PRIMARY index being used,
resulting in a long scan in newer categories where all the linter_id are
higher.

Bug: T200517
Change-Id: I373692942121ff555565c9c2c310087cd097ef21
---
 includes/ApiQueryLintErrors.php | 12 +++++++++++-
 includes/LintErrorsPager.php    | 11 +++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/includes/ApiQueryLintErrors.php b/includes/ApiQueryLintErrors.php
index 8cc4a47b..134f4db5 100644
--- a/includes/ApiQueryLintErrors.php
+++ b/includes/ApiQueryLintErrors.php
@@ -51,11 +51,14 @@ class ApiQueryLintErrors extends ApiQueryBase {
 		$this->requireMaxOneParameter( $params, 'pageid', 'title' );
 		$this->requireMaxOneParameter( $params, 'namespace', 'title' );
 
+		$useIndex = true;
 		$categories = $params['categories'];
 		if ( !$categories ) {
 			$categories = $this->categoryManager->getVisibleCategories();
 		}
-
+		if ( count( $categories ) > 1 ) {
+			$useIndex = false;
+		}
 		$this->addTables( 'linter' );
 		$this->addWhereFld( 'linter_cat', array_values( $this->categoryManager->getCategoryIds(
 			$categories
@@ -67,14 +70,17 @@ class ApiQueryLintErrors extends ApiQueryBase {
 		if ( $params['pageid'] !== null ) {
 			// This can be an array or a single pageid
 			$this->addWhereFld( 'linter_page', $params['pageid'] );
+			$useIndex = false;
 		}
 		if ( $params['namespace'] !== null ) {
 			$this->addWhereFld( 'page_namespace', $params['namespace'] );
+			$useIndex = false;
 		}
 		if ( $params['title'] !== null ) {
 			$title = $this->getTitleFromTitleOrPageId( [ 'title' => $params['title'] ] );
 			$this->addWhereFld( 'page_namespace', $title->getNamespace() );
 			$this->addWhereFld( 'page_title', $title->getDBkey() );
+			$useIndex = false;
 		}
 		$this->addTables( 'page' );
 		$this->addJoinConds( [ 'page' => [ 'INNER JOIN', 'page_id=linter_page' ] ] );
@@ -83,6 +89,10 @@ class ApiQueryLintErrors extends ApiQueryBase {
 			'linter_start', 'linter_end',
 			'page_namespace', 'page_title',
 		] );
+		if ( $useIndex ) {
+			// T200517#10236299: Force the use of the category index
+			$this->addOption( 'USE INDEX', [ 'linter' => 'linter_cat_page_position' ] );
+		}
 		// Be explicit about ORDER BY
 		$this->addOption( 'ORDER BY', 'linter_id' );
 		// Add +1 to limit to know if there's another row for continuation
diff --git a/includes/LintErrorsPager.php b/includes/LintErrorsPager.php
index 9f65173d..b0d491d5 100644
--- a/includes/LintErrorsPager.php
+++ b/includes/LintErrorsPager.php
@@ -116,6 +116,8 @@ class LintErrorsPager extends TablePager {
 			] )
 			->where( [ 'linter_cat' => $this->categoryId ] );
 
+		$useIndex = false;
+
 		if ( $this->title !== '' ) {
 			$namespaces = $this->namespaces ?: [ NS_MAIN ];
 			// Specify page_namespace so that the index can be used (T360865)
@@ -134,15 +136,24 @@ class LintErrorsPager extends TablePager {
 			}
 		} elseif ( $this->namespaces ) {
 			$queryBuilder->where( [ 'linter_namespace' => $this->namespaces ] );
+		} else {
+			$useIndex = true;
 		}
 
 		if ( $this->throughTemplate !== 'all' ) {
+			$useIndex = false;
 			$op = ( $this->throughTemplate === 'with' ) ? '!=' : '=';
 			$queryBuilder->where( $this->mDb->expr( 'linter_template', $op, '' ) );
 		}
 		if ( $this->tag !== 'all' && ( new HtmlTags( $this ) )->checkAllowedHTMLTags( $this->tag ) ) {
+			$useIndex = false;
 			$queryBuilder->where( [ 'linter_tag'  => $this->tag ] );
 		}
+
+		if ( $useIndex ) {
+			// T200517#10236299: Force the use of the category index
+			$queryBuilder->option( 'USE INDEX', [ 'linter' => 'linter_cat_page_position' ] );
+		}
 	}
 
 	/**