Re: Psql or test application hangs when interface is down for the DB server

Currently the test application or the psql will unblock after ~15
minutes. This is a very huge time to realize for programs this situation
which do database updates.
As far as I have debugged, I see that the execution is waiting on
'poll()' system call in the function pqSocketPoll() which is called as a
result of 'PQexec()' and the timeout paramater provided will be -1,
which means infinite wait time. It not clear how this is getting
unblocked after 15 minutes. Who will write to the socket or who will
interrupt the poll() system call?

Is there any other workaround or alternative so that the situation about
the interface is down is known and based on that the 'PQexec' does not
get blocked for ~15 minutes.

regards,
Niranjan

-----Original Message-----
From: ext Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
Sent: Tuesday, July 15, 2008 8:16 PM
To: K, Niranjan (NSN - IN/Bangalore)
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: [BUGS] Psql or test application hangs when interface is
down for the DB server

"K, Niranjan (NSN - IN/Bangalore)" <niranjan(dot)k(at)nsn(dot)com> writes:
> In the postgres database there is table 'COUNTER_TABLE' with column
> integer type 'COUNTER'. The test application attached in this mail,
> will start a transaction, gets the current value in the COUNTER,
> increments the value and updates the incremented value into the
COUNTER column.
> This is being done in a loop. The program is started in a remote
> client and after few transactions, the interface between the client &
> the database server is brought down (example I used "ifconfig eth0
> down" in the server). With this the test application hangs and does
> not return from the API of postgres (ex. 'PQexec').

If you waited long enough for the TCP connection to time out, it would
return (with an error, of course). This behavior is not a bug, it is
the expected behavior of any program using a network connection.

regards, tom lane