check_key_changes

Default: False (True when using version 6.1 or later of the Host or Enterprise Server)
Range: True or False

When set to True, this parameter tells the program to set the DSOPT_CheckKeyChanges bit (DATASETS client control table, “ds_options”) to the value of the DSFLG_Key_Chg_Allowed bit (DATASETS client control table, “misc_flags”). This causes the client to request that DBEngine send it all updates for such data sets as BI/AI(Before-Image/After-Image) pairs. The Client can then determine if any of the values of the key items changes and if so do a delete/insert instead of an update.

If you use version 6.1 of the Host or Enterprise Server, this parameter operates differently. The client registers all of the keys it uses with the engine (DBEngine or Enterprise) and the engine checks the values of the keys in the before- and after-images in the audit file. If the keys are unchanged, the engine sends the Client a MODIFY record, as it would for any normal update. Conversely, if the keys change, the engine sends the Client both the before- and the after-image so that it can delete the old record and replace it with the new one. This enhancement has significant effects on performance as it usually cuts the TCP/IP traffic in half for updates to such data sets.