RE: Timeout parameters - Mailing list pgsql-hackers

From: Jamison, Kirk [mailto:k.jamison@jp.fujitsu.com]
> 1) tcp_user_timeout parameter
> I think this can be "committed" separately when it's finalized.

Do you mean you've reviewed and tested the patch by simulating a communication failure in the way Nagaura-san
suggested?


> 2) tcp_socket_timeout parameter
> - whether (a) it should abort the connection from pqWait() or
>   other means, or 
> (b) cancel the statement similar to how psql
>   does it as suggested by Fabien

We have no choice but to terminate the connection, because we can't tell whether we can recover from the problem and
continueto use the connection (e.g. long-running query) or not (permanent server or network failure).
 

Regarding the place, pqWait() is the best (and possibly only) place.  The purpose of this feature is to avoid waiting
forresponse from the server forever (or too long) in any case, as a last resort.
 

Oracle has similar parameters called SQLNET.RECV_TIMEOUT and SQLNET.SEND_TIMEOUT.  From those names, I guess they use
SO_RCVTIMEOand SO_SNDTIMEO socket options.  However, we can't use them because use non-blocking sockets and poll(),
whileSO_RCV/SND_TIMEO do ont have an effect for poll():
 

[excerpt from "man 7 socket"]
--------------------------------------------------
       SO_RCVTIMEO and SO_SNDTIMEO
          Specify the receiving or sending  timeouts  until  reporting  an
          error.  The argument is a struct timeval.  If an input or output
          function blocks for this period of time, and data has been  sent
          or  received,  the  return  value  of  that function will be the
          amount of data transferred; if no data has been transferred  and
          the  timeout has been reached then -1 is returned with errno set
          to EAGAIN or EWOULDBLOCK just as if the socket was specified  to
          be  non-blocking.   If  the timeout is set to zero (the default)
          then the operation  will  never  timeout.   Timeouts  only  have
          effect  for system calls that perform socket I/O (e.g., read(2),
          recvmsg(2), send(2), sendmsg(2)); timeouts have  no  effect  for
          select(2), poll(2), epoll_wait(2), etc.
--------------------------------------------------



> - proper parameter name
> 
> Based from your description below, I agree with Fabien that it's somehow
> the application/client side query timeout

I think the name is good because it indicates the socket-level timeout.  That's just like PgJDBC and Oracle, and I
didn'tfeel strange when I read their manuals.
 


> Perhaps you could also clarify a bit more through documentation on how
> socket_timeout handles the timeout differently from statement_timeout
> and tcp_user_timeout.

Maybe.  Could you suggest good description?


Regards
Takayuki Tsunakawa