In most cases, all calls support a MessageID element in the request
and a CorrelationID element in the response. If you pass a message
ID in a request, we will return the same value in CorrelationID in
the response. You can use this for tracking that a response is
returned for every request and to match particular responses to
particular requests. If you do not pass MessageID in the request,
CorrelationID is not returned. Note that some calls are designed to
retrieve large sets of meta-data that only change once a day or less
often. To improve performance, these calls return cached responses
when you request all available data (with no filters). In these
cases, the correlation ID is not applicable. However, if you specify
an input filter to reduce the amount data returned, you can use
MessageID and CorrelationID for these meta-data calls.
These are the calls that can return cached responses
GetCategories, GetAttributesCS, GetCategory2CS, GetAttributesXsl,
GetProductFinder, GetProductFinderXsl, and GetProductSearchPage.