Cleanup DatabaseBase::query implicit transaction code

* Add DatabaseBase::isTransactableQuery() for checking whether a query could
  benefit from being executed in a transaction.

Change-Id: Ie5b116bc726b47c68459e6525a1bb43b96bd9f30

diff --git a/includes/db/Database.php b/includes/db/Database.php
index 2182b2c..7938ce6 100644 (file)
--- a/includes/db/Database.php
+++ b/includes/db/Database.php
@@ -1039,6 +1039,20 @@ abstract class DatabaseBase implements IDatabase {
                return !preg_match( '/^(?:SELECT|BEGIN|ROLLBACK|COMMIT|SET|SHOW|EXPLAIN|\(SELECT)\b/i', $sql );
        }
 
+       /**
+        * Determine whether a SQL statement is sensitive to isolation level.
+        * A SQL statement is considered transactable if its result could vary
+        * depending on the transaction isolation level. Operational commands
+        * such as 'SET' and 'SHOW' are not considered to be transactable.
+        *
+        * @param string $sql
+        * @return bool
+        */
+       public function isTransactableQuery( $sql ) {
+               $verb = substr( $sql, 0, strcspn( $sql, " \t\r\n" ) );
+               return !in_array( $verb, array( 'BEGIN', 'COMMIT', 'ROLLBACK', 'SHOW', 'SET' ) );
+       }
+
        /**
         * Run an SQL query and return the result. Normally throws a DBQueryError
         * on failure. If errors are ignored, returns false instead.
@@ -1088,21 +1102,12 @@ abstract class DatabaseBase implements IDatabase {
                // Or, for one-word queries (like "BEGIN" or COMMIT") add it to the end (bug 42598)
                $commentedSql = preg_replace( '/\s|$/', " /* $fname $userName */ ", $sql, 1 );
 
-               # If DBO_TRX is set, start a transaction
-               if ( ( $this->mFlags & DBO_TRX ) && !$this->mTrxLevel &&
-                       $sql != 'BEGIN' && $sql != 'COMMIT' && $sql != 'ROLLBACK'
-               ) {
-                       # Avoid establishing transactions for SHOW and SET statements too -
-                       # that would delay transaction initializations to once connection
-                       # is really used by application
-                       $sqlstart = substr( $sql, 0, 10 ); // very much worth it, benchmark certified(tm)
-                       if ( strpos( $sqlstart, "SHOW " ) !== 0 && strpos( $sqlstart, "SET " ) !== 0 ) {
-                               if ( $wgDebugDBTransactions ) {
-                                       wfDebug( "Implicit transaction start.\n" );
-                               }
-                               $this->begin( __METHOD__ . " ($fname)" );
-                               $this->mTrxAutomatic = true;
+               if ( !$this->mTrxLevel && $this->getFlag( DBO_TRX ) && $this->isTransactableQuery( $sql ) ) {
+                       if ( $wgDebugDBTransactions ) {
+                               wfDebug( "Implicit transaction start.\n" );
                        }
+                       $this->begin( __METHOD__ . " ($fname)" );
+                       $this->mTrxAutomatic = true;
                }
 
                # Keep track of whether the transaction has write queries pending