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 call CHECK_FOR_INTERRUPTS here? */
CHECK_FOR_INTERRUPTS();
}
}

best regards,
Florian Pflug