Re: [HACKERS] [PATCH v1] Add and report the new "in_hot_standby"GUC pseudo-variable.

From: pgsql-hackers-owner@postgresql.org
> [mailto:pgsql-hackers-owner@postgresql.org] On Behalf Of Tom Lane
> I didn't look at exactly how you tried to do that, but GUCs whose values
> depend on other GUCs generally don't work well at all.

transaction_read_only and transaction_isolation depends on default_transaction_read_only and
default_transaction_isolationrespectively.  But I feel you are concerned about something I'm not aware of.  Could you
shareyour worries?  I haven't found a problem so far.
 


> >> * Its value is false during recovery.
> 
> [ scratches head... ]  Surely this should read as "true" during recovery?

Ouch, you are right.


> Also, what happens if the standby server goes live mid-session?

The clients will know the change of session_read_only when they do something that calls RecoveryInProgress().
Currently,RecoveryInProgress() seems to be the only place where the sessions notice the promotion, so I set
session_read_onlyto the value of default_transaction_read_only there.  I think that there is room for discussion here.
Itwould be ideal for the sessions to notice the server promotion promptly and notify the clients of the change.  I have
noidea to do that well.
 

Regards
Takayuki Tsunakawa