Caching of data

By default Web Maps caches data in order to avoid repeatedly querying data sources. This increases response speed and reduces load on the data sources themselves. The cache is self-cleansing: typically it will remove any unused cached data that is older than 15 minutes.

Caching however has three side effects of which administrators need to be aware:

1. Repeated queries using the same criteria may not flush the cache, meaning that changed data in the data source may not immediately appear on the map.
2. If an error occurs with a data source (e.g. network connectivity is lost), the fault condition may itself be cached some time after the fault has been resolved. This is particularly likely when activity is light on the system (because the fault condition doesn't get flushed as the system remains unused for an extended period of time and the first 're-use' is to the faulty source with the same query).
3. If a user leaves a session for a long time (longer than 15 minutes) and then attempts to return to it, the session may have been cleaned out forcing the user to redo their query.

Nothing can be done about sessions timing out (the system has to reclaim disk space held by potentially defunct sessions), however if a cache needs to be forcibly flushed (usually during testing or recovering from faults) this can be done manually by calling the url:

http://HOST/emuwebXXXX/webservices/lib/DataCacher.php?action=cleanCache&test=true&testCall=true