Re: read() returns ERANGE in Mac OS X

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Sun, May 20, 2012 at 2:12 PM, Alvaro Herrera
> <alvherre(at)commandprompt(dot)com> wrote:
>>> Yeah, an enum would be nicer than an additional GUC. I kinda keep forgetting
>>> that we have those. Though to bikeshed, the GUC should probably be just called
>>> 'zero_pages' and take the values 'never', 'missing', 'unreadable' ;-)

>> Sounds reasonable to me ..

> It seems like it would be nicer to have a setting that somehow makes
> the system disregard errors and soldier on rather than actively
> destroying your data. Not that I have an exact design in mind, but
> zero_damaged_pages is a really fast way to destroy your data.

If we were sure that the kernel error was permanent, then this argument
would be moot: the data is gone already. The scary thought here is that
it might be a transient error, such as a not-always-repeatable kernel
bug. In that case, zeroing the page would indeed lose data that had
been recoverable before.

I'm not entirely sure how we would "soldier on" though; there is no good
reason to think that the kernel has loaded any data at all into
userspace when read() fails.

regards, tom lane