You can obtain the file_id from the SYSDBSPACE system view. The estimates returned by the sa_get_dtt_groupreads system procedure are part of the cost
model, and are used to select group reads of appropriate sizes during operations such as sorting.
This procedure, intended for internal diagnostic purposes, retrieves data from the ISYSOPTSTAT system table. Rows are not
returned if the specified dbspace does not have any estimates recorded in SYSOPTSTAT. To tailor estimates for specific hardware
devices, execute the following statement: