I feel this is introduces to consider some default
ExtraSysTablePrefixes I am not sure in which case it will be used. As for as i understand there will be no User specific system table considered in Postgres prefixing with "dd_". So there is no point to keep this extra psqlODBC config parameter in future.
I can find it only at the following two places in the psqlodbc branch
1) in dlg_specific.h
#define DEFAULT_EXTRASYSTABLEPREFIXES "dd_"
2) In dlg_specific.c
/* Extra Systable prefixes */
/*
* Use @@@ to distinguish between blank extra prefixes and no key
* entry
*/
SQLGetPrivateProfileString(section, INI_EXTRASYSTABLEPREFIXES, "@@@",
temp, sizeof(temp), filename);
if (strcmp(temp, "@@@"))
strcpy(comval->extra_systable_prefixes, temp);
else if (inst_position)
strcpy(comval->extra_systable_prefixes, DEFAULT_EXTRASYSTABLEPREFIXES);
mylog("ci=%p globals.extra_systable_prefixes = '%s'\n", ci, comval->extra_systable_prefixes);