#633678 by Josh Waihi, chx, Crell, David Strauss, and Damien Tournoud: Make sequence API work on non-MySQL databases.

1 files changed, 48 insertions, 0 deletions

diff --git a/includes/database/pgsql/database.inc b/includes/database/pgsql/database.inc
index 8b60b957b..218d10865 100644
--- a/includes/database/pgsql/database.inc
+++ b/includes/database/pgsql/database.inc
@@ -11,6 +11,11 @@
  * @{
  */
 
+/**
+ * The name by which to obtain a lock for retrive the next insert id.
+ */
+define('POSTGRESQL_NEXTID_LOCK', 1000);
+
 class DatabaseConnection_pgsql extends DatabaseConnection {
 
   public function __construct(array $connection_options = array()) {
@@ -127,6 +132,49 @@ class DatabaseConnection_pgsql extends DatabaseConnection {
 
     return isset($specials[$operator]) ? $specials[$operator] : NULL;
   }
+
+  /**
+   * Retrive a the next id in a sequence.
+   *
+   * PostgreSQL has built in sequences. We'll use these instead of inserting
+   * and updating a sequences table.
+   */
+  public function nextId($existing = 0) {
+
+    // Retrive the name of the sequence. This information cannot be cached 
+    // because the prefix may change, for example, like it does in simpletests.
+    $sequence_name = $this->makeSequenceName('sequences', 'value');
+
+    // When PostgreSQL gets a value too small then it will lock the table, 
+    // retry the INSERT and if it's still too small then alter the sequence. 
+    $id = $this->query("SELECT nextval('" . $sequence_name . "')")->fetchField();
+    if ($id > $existing) {
+      return $id;
+    }
+
+    // PostgreSQL advisory locks are simply locks to be used by an
+    // application such as Drupal. This will prevent other Drupal proccesses
+    // from altering the sequence while we are. 
+    $this->query("SELECT pg_advisory_lock(" . POSTGRESQL_NEXTID_LOCK . ")");
+
+    // While waiting to obtain the lock, the sequence may have been altered
+    // so lets try again to obtain an adequate value.
+    $id = $this->query("SELECT nextval('" . $sequence_name . "')")->fetchField();
+    if ($id > $existing) {
+      $this->query("SELECT pg_advisory_unlock(" . POSTGRESQL_NEXTID_LOCK . ")");
+      return $id;
+    }
+
+    // Reset the sequence to a higher value than the existing id.
+    $this->query("ALTER SEQUENCE " . $sequence_name . " RESTART WITH " . ($existing + 1));
+
+    // Retrive the next id. We know this will be as high as we want it.
+    $id = $this->query("SELECT nextval('" . $sequence_name . "')")->fetchField();
+
+    $this->query("SELECT pg_advisory_unlock(" . POSTGRESQL_NEXTID_LOCK . ")");
+
+    return $id;
+  }
 }
 
 /**