Re: High CPU shoot during poll retry

On 12/12/2014 12:31 PM, Gaurav Srivastava wrote:

Hi All,

In ODBC library later to change done as part of commit Title  "Rip out
broken retry/timeout logic in SOCK_wait_for_ready." in file socket.c

Now  the cpde snippet for SOCK_wait_for_ready() is like:

        do {
#ifdef  HAVE_POLL
                 fds.fd = sock->socket;
                 fds.events = output ? POLLOUT : POLLIN;
                 fds.revents = 0;
               *  ret = poll(&fds, 1, nowait ? 0 : -1); *
mylog("!!!  poll ret=%d revents=%x\n", ret, fds.revents);
#else
                 FD_ZERO(&fds);
                 FD_ZERO(&except_fds);
                 FD_SET(sock->socket, &fds);
                 FD_SET(sock->socket, &except_fds);
                 if (nowait)
                 {
                         tm.tv_sec = 0;
                         tm.tv_usec = 0;
                 }
                 ret = select((int) sock->socket + 1, output ? NULL : &fds,
output ? &fds : NULL, &except_fds, nowait ? &tm : NULL);
#endif /* HAVE_POLL */
                 gerrno = SOCK_ERRNO;
         } *while (ret < 0 && EINTR == gerrno);*



So whenever there is no fd is ready to be read it will immediately return
and solve the issue of infinite query hung but  due to immediate return it
will go for continuous retries and causing CPU to shoot very high.This is
one of the case we are suffering in our scenario after upgrading ODBC.

Why do you think it will go into continuous retries?

- Heikki