[9.2] Confusion over CacheRegisterSyscacheCallback

Commit b5282aa893:
"Revise sinval code to remove no-longer-used tuple TID from inval messages."

dropped ItemPointer from callbacks and replaced it with "hashValue".
There seems to be 2 ways that new backend code calculates it:

- hashoid(oid), which seems to assume too much?
- CatalogCacheComputeTupleHashValue(), which is 'static'.

So my question is that after doing generic SearchSysCache() like:

tup = SearchSysCache(USERMAPPINGUSERSERVER,
ObjectIdGetDatum(user_mapping->userid),
ObjectIdGetDatum(foreign_server->serverid),
0, 0);

what is the proper way to calculate the hashValue that
will be given to callback?

--
marko