diff --git a/core/lib/Drupal/Core/Database/Driver/pgsql/Upsert.php b/core/lib/Drupal/Core/Database/Driver/pgsql/Upsert.php
index a0a9de8..e23092d 100644
--- a/core/lib/Drupal/Core/Database/Driver/pgsql/Upsert.php
+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Upsert.php
@@ -29,68 +29,38 @@ public function execute() {
 
     // Default fields are always placed first for consistency.
     $insert_fields = array_merge($this->defaultFields, $this->insertFields);
-    $insert_fields_escaped = array_map(function($f) { return $this->connection->escapeField($f); }, $insert_fields);
 
     $table = $this->connection->escapeTable($this->table);
-    $unique_key = $this->connection->escapeField($this->key);
 
     // We have to execute multiple queries, therefore we wrap everything in a
     // transaction so that it is atomic where possible.
     $transaction = $this->connection->startTransaction();
 
     try {
-      // First, create a temporary table with the same schema as the table we
-      // are trying to upsert in. This results in the following query:
-      //
-      // CREATE TEMP TABLE temp_table AS SELECT * FROM table_name LIMIT 0;
-      $query = 'SELECT * FROM {' . $table . '} LIMIT 0';
-      $temp_table = $this->connection->queryTemporary($query, [], $this->queryOptions);
-
-      // Second, insert the data in the temporary table.
-      $insert = $this->connection->insert($temp_table, $this->queryOptions)
-        ->fields($insert_fields);
+      // First, lock the table we're upserting into.
+      $this->connection->query('LOCK TABLE {' . $table . '} IN SHARE ROW EXCLUSIVE MODE', [], $this->queryOptions);
+
+      // Second, delete all items first so we can do one insert.
+      $unique_key_position = array_search($this->key, $insert_fields);
+      $delete_ids = [];
       foreach ($this->insertValues as $insert_values) {
-        $insert->values($insert_values);
+        $delete_ids[] = $insert_values[$unique_key_position];
       }
-      $insert->execute();
 
-      // Third, lock the table we're upserting into.
-      $this->connection->query('LOCK TABLE {' . $table . '} IN EXCLUSIVE MODE', [], $this->queryOptions);
-
-      // Fourth, update any rows that can be updated. This results in the
-      // following query:
-      //
-      // UPDATE table_name
-      // SET column1 = temp_table.column1 [, column2 = temp_table.column2, ...]
-      // FROM temp_table
-      // WHERE table_name.id = temp_table.id;
-      $update = [];
-      foreach ($insert_fields_escaped as $field) {
-        if ($field !== $unique_key) {
-          $update[] = "$field = {" . $temp_table . "}.$field";
-        }
+      // Delete in chunks when a large array is passed.
+      foreach (array_chunk($delete_ids, 1000) as $delete_ids_chunk) {
+        $this->connection->delete($this->table, $this->queryOptions)
+          ->condition($this->key, $delete_ids_chunk, 'IN')
+          ->execute();
       }
 
-      $update_query = 'UPDATE {' . $table . '} SET ' . implode(', ', $update);
-      $update_query .= ' FROM {' . $temp_table . '}';
-      $update_query .= ' WHERE {' . $temp_table . '}.' . $unique_key . ' = {' . $table . '}.' . $unique_key;
-      $this->connection->query($update_query, [], $this->queryOptions);
-
-      // Fifth, insert the remaining rows. This results in the following query:
-      //
-      // INSERT INTO table_name
-      // SELECT temp_table.primary_key, temp_table.column1 [, temp_table.column2 ...]
-      // FROM temp_table
-      // LEFT OUTER JOIN table_name ON (table_name.id = temp_table.id)
-      // WHERE table_name.id IS NULL;
-      $select = $this->connection->select($temp_table, 'temp_table', $this->queryOptions)
-        ->fields('temp_table', $insert_fields);
-      $select->leftJoin($this->table, 'actual_table', 'actual_table.' . $this->key . ' = temp_table.' . $this->key);
-      $select->isNull('actual_table.' . $this->key);
-
-      $this->connection->insert($this->table, $this->queryOptions)
-        ->from($select)
-        ->execute();
+      // Third, insert all the values.
+      $insert = $this->connection->insert($this->table, $this->queryOptions)
+        ->fields($insert_fields);
+      foreach ($this->insertValues as $insert_values) {
+        $insert->values($insert_values);
+      }
+      $insert->execute();
     }
     catch (\Exception $e) {
       // One of the queries failed, rollback the whole batch.