Re: Patch to improve reliability of postgresql on linux nfs

On Sep13, 2011, at 13:07 , Florian Pflug wrote:
> Here's my suggested implementation for pg_write_nointr. pg_read_nointr should be similar
> (but obviously without the ENOSPC handling)
>
> <wrong pg_write_nointr implementation snipped>

Sorry for the self-reply. I realized only after hitting send that I
got the ENOSPC handling wrong again - we probably ought to check for
ENOSPC as well as ret == 0. Also, it seems preferable to return the
number of bytes actually written instead of -1 if we hit an error during
retry.

With this version, any return value other than <amount> signals an
error, the number of actually written bytes is reported even in the
case of an error (to the best of pg_write_nointr's knowledge), and
errno always indicates the kind of error.

int pg_write_nointr(int fd, const void *bytes, Size amount)
{int written = 0;
while (amount > 0){  int ret;
  ret = write(fd, bytes, amount);
  if ((ret < 0) && (errno == EINTR))  {    /* interrupted by signal before first byte was written. Retry */
    /* XXX: Is it safe to call CHECK_FOR_INTERRUPTS here? */    CHECK_FOR_INTERRUPTS();
    continue;  }  else if (ret < 1)  {    /* error occurred. Abort */
    if (ret == 0)      /* out of disk space */      errno = ENOSPC;
    if (written == 0)      return -1;    else      return written;  }
  /* made progress */  written += ret;  amount -= ret;  bytes = (const char *) bytes + ret;    /* XXX: Is it safe to
callCHECK_FOR_INTERRUPTS here? */  CHECK_FOR_INTERRUPTS();} 
}

best regards,
Florian Pflug