MDL-17020 dml: native pgsql driver - implementation and unittests of transactions

lib/dml/pgsql_native_moodle_database.php

@@ -1036,4 +1036,47 @@ class pgsql_native_moodle_database extends moodle_database {
         return $positivematch ? '~*' : '!~*';
     }
 
+/// transactions
+    /**
+     * on DBs that support it, switch to transaction mode and begin a transaction
+     * you'll need to ensure you call commit_sql() or your changes *will* be lost.
+     *
+     * this is _very_ useful for massive updates
+     */
+    public function begin_sql() {
+        $sql = "BEGIN ISOLATION LEVEL READ COMMITTED";
+        $result = pg_query($this->pgsql, $sql);
+        if ($result === false) {
+            return false;
+        }
+        pg_free_result($result);
+        return true;
+    }
+
+    /**
+     * on DBs that support it, commit the transaction
+     */
+    public function commit_sql() {
+        $sql = "COMMIT";
+        $result = pg_query($this->pgsql, $sql);
+        if ($result === false) {
+            return false;
+        }
+        pg_free_result($result);
+        return true;
+    }
+
+    /**
+     * on DBs that support it, rollback the transaction
+     */
+    public function rollback_sql() {
+        $sql = "ROLLBACK";
+        $result = pg_query($this->pgsql, $sql);
+        if ($result === false) {
+            return false;
+        }
+        pg_free_result($result);
+        return true;
+    }
+
 }