LOB and XML data and its effect on block fetch for DRDA

For a non-scrollable blocked cursor, the server sends all the non-LOB and non-XML data columns for a block of rows in one message, including LOB locator values.

As each row is fetched by the application, the requester obtains the non-LOB data columns directly from the query block. If the row contains non-null and non-zero length LOB values, those values are retrieved from the server at that time. This behavior limits the impact to the network by pacing the amount of data that is returned at any one time. If all LOB data columns are retrieved into LOB locator host variables or if the row does not contain any non-null or non-zero length LOB columns, then the whole row can be retrieved directly from the query block.

For a scrollable blocked cursor, the LOB data columns are returned at the same time as the non-LOB and non XML data columns. When the application fetches a row that is in the block, a separate message is not required to get the LOB columns.