From 70ed89ad436f9a5c9090e9927c40a701db6cf93f Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Tue, 17 Jul 2018 21:22:59 +0100
Subject: [PATCH] Reduce the rate of calls to Category::refreshCounts

Bug: T199762
Change-Id: I23e2e1ebf187d21ea4bd22304aa622199a8b9c5b
---
 includes/Category.php                     | 41 +++++++++++++++++++++++
 includes/deferred/LinksDeletionUpdate.php | 32 ++----------------
 includes/page/WikiPage.php                | 21 +++---------
 3 files changed, 47 insertions(+), 47 deletions(-)

diff --git a/includes/Category.php b/includes/Category.php
index f8ac8aeb59..3352c2c2b0 100644
--- a/includes/Category.php
+++ b/includes/Category.php
@@ -420,4 +420,45 @@ class Category {
 
 		return true;
 	}
+
+	/**
+	 * Call refreshCounts() if there are no entries in the categorylinks table
+	 * or if the category table has a row that states that there are no entries
+	 *
+	 * Due to lock errors or other failures, the precomputed counts can get out of sync,
+	 * making it hard to know when to delete the category row without checking the
+	 * categorylinks table.
+	 *
+	 * @return bool Whether links were refreshed
+	 * @since 1.32
+	 */
+	public function refreshCountsIfEmpty() {
+		$dbw = wfGetDB( DB_MASTER );
+
+		$hasLink = $dbw->selectField(
+			'categorylinks',
+			'1',
+			[ 'cl_to' => $this->getName() ],
+			__METHOD__
+		);
+		if ( !$hasLink ) {
+			$this->refreshCounts(); // delete any category table entry
+
+			return true;
+		}
+
+		$hasBadRow = $dbw->selectField(
+			'category',
+			'1',
+			[ 'cat_title' => $this->getName(), 'cat_pages <= 0' ],
+			__METHOD__
+		);
+		if ( $hasBadRow ) {
+			$this->refreshCounts(); // clean up this row
+
+			return true;
+		}
+
+		return false;
+	}
 }
diff --git a/includes/deferred/LinksDeletionUpdate.php b/includes/deferred/LinksDeletionUpdate.php
index 9f6257c810..f370e43ffd 100644
--- a/includes/deferred/LinksDeletionUpdate.php
+++ b/includes/deferred/LinksDeletionUpdate.php
@@ -101,7 +101,8 @@ class LinksDeletionUpdate extends DataUpdate implements EnqueueableDataUpdate {
 		if ( $title->getNamespace() === NS_CATEGORY ) {
 			// T166757: do the update after the main job DB commit
 			DeferredUpdates::addCallableUpdate( function () use ( $title ) {
-				$this->refreshCategoryIfEmpty( $title );
+				$cat = Category::newFromName( $title->getDBkey() );
+				$cat->refreshCountsIfEmpty();
 			} );
 		}
 
@@ -187,35 +188,6 @@ class LinksDeletionUpdate extends DataUpdate implements EnqueueableDataUpdate {
 		ScopedCallback::consume( $scopedLock );
 	}
 
-	/**
-	 * @param Title $title
-	 */
-	private function refreshCategoryIfEmpty( Title $title ) {
-		$dbw = $this->getDB();
-
-		$row = $dbw->selectRow(
-			'category',
-			[ 'cat_id', 'cat_title', 'cat_pages', 'cat_subcats', 'cat_files' ],
-			[ 'cat_title' => $title->getDBkey(), 'cat_pages <= 100' ],
-			__METHOD__
-		);
-
-		if ( !$row ) {
-			return; // nothing to delete
-		}
-
-		$cat = Category::newFromRow( $row, $title );
-		$hasLink = $dbw->selectField(
-			'categorylinks',
-			'1',
-			[ 'cl_to' => $title->getDBkey() ],
-			__METHOD__
-		);
-		if ( !$hasLink ) {
-			$cat->refreshCounts(); // delete the category table entry
-		}
-	}
-
 	private function batchDeleteByPK( $table, array $conds, array $pk, $bSize ) {
 		$services = MediaWikiServices::getInstance();
 		$lbFactory = $services->getDBLoadBalancerFactory();
diff --git a/includes/page/WikiPage.php b/includes/page/WikiPage.php
index 7cc25bd3fc..0a80892eb1 100644
--- a/includes/page/WikiPage.php
+++ b/includes/page/WikiPage.php
@@ -3343,23 +3343,10 @@ class WikiPage implements Page, IDBAccessObject {
 		foreach ( $deleted as $catName ) {
 			$cat = Category::newFromName( $catName );
 			Hooks::run( 'CategoryAfterPageRemoved', [ $cat, $this, $id ] );
-		}
-
-		// Refresh counts on categories that should be empty now
-		if ( count( $deleted ) ) {
-			$rows = $dbw->select(
-				'category',
-				[ 'cat_id', 'cat_title', 'cat_pages', 'cat_subcats', 'cat_files' ],
-				[ 'cat_title' => $deleted, 'cat_pages <= 100' ],
-				__METHOD__
-			);
-			foreach ( $rows as $row ) {
-				$cat = Category::newFromRow( $row );
-				// T166757: do the update after this DB commit
-				DeferredUpdates::addCallableUpdate( function () use ( $cat ) {
-					$cat->refreshCounts();
-				} );
-			}
+			// Refresh counts on categories that should be empty now (after commit, T166757)
+			DeferredUpdates::addCallableUpdate( function () use ( $cat ) {
+				$cat->refreshCountsIfEmpty();
+			} );
 		}
 	}
 
-- 
2.20.1