Re: Patch to improve reliability of postgresql on linux nfs

On Tue, Sep 13, 2011 at 01:30:34PM +0200, Florian Pflug wrote:
> 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 call CHECK_FOR_INTERRUPTS here? */
> CHECK_FOR_INTERRUPTS();
> }
> }
>
> best regards,
> Florian Pflug
>

It will be interesting to see if there are any performance ramifications to
this new write function.

Regards,
Ken