Setting control structure information field values
isc_blob_ctl structure contains three fields that store information about the Blob currently being accessed:
You should attempt to maintain correct values for these fields in the filter function, whenever possible. Depending on the purpose of the filter, maintaining correct values for the fields is not always possible. For example, a filter that compresses data on a segment-by-segment basis cannot determine the size of
ctl_max_segment until it processes all segments.
These fields are informational only. InterBase does not use the values of these fields in internal processing.