From 0352fe44f10fa2a20027b6ca7d583232019781cb Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Tue, 27 Jun 2017 11:31:35 -0700
Subject: [PATCH] Avoid checking double-prefixed table names in mysql
 tableExists()

Change-Id: I9d91a5305227171d0776ffa443d4e538fbe1b15f
---
 includes/libs/rdbms/database/Database.php     |  6 ++++--
 .../libs/rdbms/database/DatabaseMysqlBase.php | 20 +++++++++----------
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/includes/libs/rdbms/database/Database.php b/includes/libs/rdbms/database/Database.php
index afeffb3048..559c28b7ad 100644
--- a/includes/libs/rdbms/database/Database.php
+++ b/includes/libs/rdbms/database/Database.php
@@ -1822,8 +1822,10 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
 	}
 
 	/**
-	 * @param string $name Table name
-	 * @return array (DB name, schema name, table prefix, table name)
+	 * Get the table components needed for a query given the currently selected database
+	 *
+	 * @param string $name Table name in the form of db.schema.table, db.table, or table
+	 * @return array (DB name or "" for default, schema name, table prefix, table name)
 	 */
 	protected function qualifiedTableComponents( $name ) {
 		# We reverse the explode so that database.table and table both output the correct table.
diff --git a/includes/libs/rdbms/database/DatabaseMysqlBase.php b/includes/libs/rdbms/database/DatabaseMysqlBase.php
index e237ef4899..8d19bc1b34 100644
--- a/includes/libs/rdbms/database/DatabaseMysqlBase.php
+++ b/includes/libs/rdbms/database/DatabaseMysqlBase.php
@@ -527,25 +527,23 @@ abstract class DatabaseMysqlBase extends Database {
 	}
 
 	public function tableExists( $table, $fname = __METHOD__ ) {
-		$table = $this->tableName( $table, 'raw' );
-		if ( isset( $this->mSessionTempTables[$table] ) ) {
-			return true; // already known to exist and won't show in SHOW TABLES anyway
-		}
-
 		// Split database and table into proper variables as Database::tableName() returns
 		// shared tables prefixed with their database, which do not work in SHOW TABLES statements
-		list( $database, $schema, $prefix, $table ) = $this->qualifiedTableComponents( $table );
+		list( $database, , $prefix, $table ) = $this->qualifiedTableComponents( $table );
+		$tableName = "{$prefix}{$table}";
 
-		$table = $prefix . $table;
+		if ( isset( $this->mSessionTempTables[$tableName] ) ) {
+			return true; // already known to exist and won't show in SHOW TABLES anyway
+		}
 
 		// We can't use buildLike() here, because it specifies an escape character
 		// other than the backslash, which is the only one supported by SHOW TABLES
-		$encLike = $this->escapeLikeInternal( $table, '\\' );
+		$encLike = $this->escapeLikeInternal( $tableName, '\\' );
 
-		// If the database has been specified (such as for shared tables), add a FROM $database clause
+		// If the database has been specified (such as for shared tables), use "FROM"
 		if ( $database !== '' ) {
-			$database = $this->addIdentifierQuotes( $database );
-			$query = "SHOW TABLES FROM $database LIKE '$encLike'";
+			$encDatabase = $this->addIdentifierQuotes( $database );
+			$query = "SHOW TABLES FROM $encDatabase LIKE '$encLike'";
 		} else {
 			$query = "SHOW TABLES LIKE '$encLike'";
 		}
-- 
2.20.1