Issue #1839998 by wiifm, mcm.guaba, Josh Waihi, dcam: Fixed TruncateQuery implemented as 'DELETE FROM' in MySQL and SQLite, but not PostgreSQL, causing nefarious table locking.

2 files changed, 23 insertions, 27 deletions

diff --git a/includes/database/mysql/query.inc b/includes/database/mysql/query.inc
index 2609aba0c..fa698d90c 100644
--- a/includes/database/mysql/query.inc
+++ b/includes/database/mysql/query.inc
@@ -86,21 +86,7 @@ class InsertQuery_mysql extends InsertQuery {
   }
 }
 
-class TruncateQuery_mysql extends TruncateQuery {
-  public function __toString() {
-    // TRUNCATE is actually a DDL statement on MySQL, and DDL statements are
-    // not transactional, and result in an implicit COMMIT. When we are in a
-    // transaction, fallback to the slower, but transactional, DELETE.
-    if ($this->connection->inTransaction()) {
-      // Create a comment string to prepend to the query.
-      $comments = $this->connection->makeComment($this->comments);
-      return $comments . 'DELETE FROM {' . $this->connection->escapeTable($this->table) . '}';
-    }
-    else {
-      return parent::__toString();
-    }
-  }
-}
+class TruncateQuery_mysql extends TruncateQuery { }
 
 /**
  * @} End of "addtogroup database".
diff --git a/includes/database/query.inc b/includes/database/query.inc
index 8beeef1e8..66495273e 100644
--- a/includes/database/query.inc
+++ b/includes/database/query.inc
@@ -83,7 +83,7 @@ interface QueryConditionInterface {
 
   /**
    * Sets a condition that the specified subquery returns values.
-   * 
+   *
    * @param SelectQueryInterface $select
    *   The subquery that must contain results.
    *
@@ -91,10 +91,10 @@ interface QueryConditionInterface {
    *   The called object.
    */
   public function exists(SelectQueryInterface $select);
-  
+
   /**
    * Sets a condition that the specified subquery returns no values.
-   * 
+   *
    * @param SelectQueryInterface $select
    *   The subquery that must not contain results.
    *
@@ -102,7 +102,7 @@ interface QueryConditionInterface {
    *   The called object.
    */
   public function notExists(SelectQueryInterface $select);
-  
+
   /**
    * Gets a complete list of all conditions in this conditional clause.
    *
@@ -283,14 +283,14 @@ abstract class Query implements QueryPlaceholderInterface {
 
   /**
    * The target of the connection object.
-   * 
+   *
    * @var string
    */
   protected $connectionTarget;
 
   /**
    * The key of the connection object.
-   * 
+   *
    * @var string
    */
   protected $connectionKey;
@@ -804,7 +804,7 @@ class DeleteQuery extends Query implements QueryConditionInterface {
     $this->condition->notExists($select);
     return $this;
   }
-  
+
   /**
    * Implements QueryConditionInterface::conditions().
    */
@@ -942,7 +942,17 @@ class TruncateQuery extends Query {
     // Create a sanitized comment string to prepend to the query.
     $comments = $this->connection->makeComment($this->comments);
 
-    return $comments . 'TRUNCATE {' . $this->connection->escapeTable($this->table) . '} ';
+    // In most cases, TRUNCATE is not a transaction safe statement as it is a
+    // DDL statement which results in an implicit COMMIT. When we are in a
+    // transaction, fallback to the slower, but transactional, DELETE.
+    // PostgreSQL also locks the entire table for a TRUNCATE strongly reducing
+    // the concurrency with other transactions.
+    if ($this->connection->inTransaction()) {
+      return $comments . 'DELETE FROM {' . $this->connection->escapeTable($this->table) . '}';
+    }
+    else {
+      return $comments . 'TRUNCATE {' . $this->connection->escapeTable($this->table) . '} ';
+    }
   }
 }
 
@@ -1053,7 +1063,7 @@ class UpdateQuery extends Query implements QueryConditionInterface {
     $this->condition->notExists($select);
     return $this;
   }
-  
+
   /**
    * Implements QueryConditionInterface::conditions().
    */
@@ -1545,7 +1555,7 @@ class MergeQuery extends Query implements QueryConditionInterface {
     $this->condition->notExists($select);
     return $this;
   }
-  
+
   /**
    * Implements QueryConditionInterface::conditions().
    */
@@ -1762,14 +1772,14 @@ class DatabaseCondition implements QueryConditionInterface, Countable {
   public function exists(SelectQueryInterface $select) {
     return $this->condition('', $select, 'EXISTS');
   }
-  
+
   /**
    * Implements QueryConditionInterface::notExists().
    */
   public function notExists(SelectQueryInterface $select) {
     return $this->condition('', $select, 'NOT EXISTS');
   }
-  
+
   /**
    * Implements QueryConditionInterface::conditions().
    */