Issue #2921855 by daffie: Default Database Schema::findTables() is slow for PostgreSQL

core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php

@@ -472,6 +472,52 @@ public function tableExists($table) {
     return (bool) $this->connection->query("SELECT 1 FROM pg_tables WHERE schemaname = :schema AND tablename = :table", [':schema' => $prefixInfo['schema'], ':table' => $prefixInfo['table']])->fetchField();
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function findTables($table_expression) {
+    $individually_prefixed_tables = $this->connection->getUnprefixedTablesMap();
+    $default_prefix = $this->connection->tablePrefix();
+    $default_prefix_length = strlen($default_prefix);
+    $tables = [];
+
+    // Load all the tables up front in order to take into account per-table
+    // prefixes. The actual matching is done at the bottom of the method.
+    $results = $this->connection->query("SELECT tablename FROM pg_tables WHERE schemaname = :schema", [':schema' => $this->defaultSchema]);
+    foreach ($results as $table) {
+      // Take into account tables that have an individual prefix.
+      if (isset($individually_prefixed_tables[$table->tablename])) {
+        $prefix_length = strlen($this->connection->tablePrefix($individually_prefixed_tables[$table->tablename]));
+      }
+      elseif ($default_prefix && substr($table->tablename, 0, $default_prefix_length) !== $default_prefix) {
+        // This table name does not start the default prefix, which means that
+        // it is not managed by Drupal so it should be excluded from the result.
+        continue;
+      }
+      else {
+        $prefix_length = $default_prefix_length;
+      }
+
+      // Remove the prefix from the returned tables.
+      $unprefixed_table_name = substr($table->tablename, $prefix_length);
+
+      // The pattern can match a table which is the same as the prefix. That
+      // will become an empty string when we remove the prefix, which will
+      // probably surprise the caller, besides not being a prefixed table. So
+      // remove it.
+      if (!empty($unprefixed_table_name)) {
+        $tables[$unprefixed_table_name] = $unprefixed_table_name;
+      }
+    }
+
+    // Convert the table expression from its SQL LIKE syntax to a regular
+    // expression and escape the delimiter that will be used for matching.
+    $table_expression = str_replace(['%', '_'], ['.*?', '.'], preg_quote($table_expression, '/'));
+    $tables = preg_grep('/^' . $table_expression . '$/i', $tables);
+
+    return $tables;
+  }
+
   /**
    * {@inheritdoc}
    */