Re: High CPU shoot during poll retry - Mailing list pgsql-odbc
| From | Gaurav Srivastava |
|---|---|
| Subject | Re: High CPU shoot during poll retry |
| Date | |
| Msg-id | CAAXqS3BFjOe8MBwprVqLwTH4BFvU55v6fGjd77XTZdj19raDuQ@mail.gmail.com Whole thread Raw |
| In response to | Re: High CPU shoot during poll retry (Heikki Linnakangas <hlinnakangas@vmware.com>) |
| Responses |
Re: High CPU shoot during poll retry
|
| List | pgsql-odbc |
We are providing timeout value as 0 or -1 in poll() timeout field meaning zero timeout or infinite wait . During zero timeout case poll will immediately return with return value as zero and come out of loop.But from the places where this api SOCK_wait_for_ready()is called , it is checked that return value is 0 or more
if (SOCK_wait_for_ready(sock, FALSE, FALSE) >= 0)
goto retry;
In case of zero timeout if reading fd is not ready, it will go into continuous retries and in case of access load suppose 200k registrations,10k calls running it will result CPU to shoot very high.if (SOCK_wait_for_ready(sock, FALSE, FALSE) >= 0)
goto retry;
Gaurav Srivastava | Associate Consultant
GlobalLogic
P +91.120.4342000.2920 M +91.9953996631 S ta5ramn1
www.globallogic.com
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On Sat, Dec 13, 2014 at 2:27 AM, Heikki Linnakangas <hlinnakangas@vmware.com> wrote:
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
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