From LimeSurvey Manual
- sessionlifetime: Defines the time in seconds after which a survey session expires. It applies only if you are using database sessions. If you do use database sessions, change the parameter in config.php or override the default value from the global settings dialog.
- memorylimit: This determines how much memory LimeSurvey can access. '128 MB' is the minimum (MB=Megabyte) recommended. If you receive time out errors or have problems generating statistics or exporting files, raise this limit to '256 MB' or higher. If your web server has set a higher limit in config.php, then this setting will be ignored.