Your test shows so SET SESSION has not transactional behaviour - the transactions fails, but the value is not reverted to NULL.
There are *two* function calls, the first fails and the second succeeds. Here is the trace with a some comments:
[...]
## SET SESSION x.x = 'null'; SET -- previous has set x.x = 'null'
## SELECT setupSecurityContext(3); -- first setup... function call NOTICE: SET secured = FALSE NOTICE: SET secured = TRUE -- there is a SET to 'ok' just after this print -- at the end the transaction fails: ERROR: insert or update on table "log" violates foreign key constraint "log_sid_fkey" DETAIL: Key (sid)=(3) is not present in table "stuff". -- no result is displayed from the SELECT
## SHOW x.x; nul -- the value is the initial value, it has been reverted
## SELECT setupSecurityContext(2); -- second setup... function call NOTICE: SET secured = FALSE NOTICE: SET secured = TRUE -- trues is displayed, the function succeeded t
## SHOW x.x; ok -- the new value is shown
ok understand
The logic depends on transactions and on nesting level (nesting doesn't depends on transactions only)
/*
* Do GUC processing at transaction or subtransaction commit or abort, or
* when exiting a function that has proconfig settings, or when undoing a
* transient assignment to some GUC variables. (The name is thus a bit of
* a misnomer; perhaps it should be ExitGUCNestLevel or some such.)
* During abort, we discard all GUC settings that were applied at nesting
* levels >= nestLevel. nestLevel == 1 corresponds to the main transaction.
*/
void
AtEOXact_GUC(bool isCommit, int nestLevel)
Probably we should to use CallXactCallbacks instead - then is not a performance impact when there are not transactional variables.