Re: read() returns ERANGE in Mac OS X

On Mon, May 21, 2012 at 12:43 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Mon, May 21, 2012 at 12:23 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> 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.
>
>> Yeah, and in fact I think that's probably not a terribly remote
>> scenario.   Also, if you're running on dying hardware, you really do
>> NOT want to force the kernel to write a whole bunch of pages back to
>> the dying disk in the midst of trying to pg_dump it before it falls
>> over.  You just want to read what you can of what's there now.
>
> Hm?  zero_damaged_pages doesn't cause the buffer to be marked dirty,
> so I dunno where these alleged writes are coming from.

I'm not sure either, but I'm pretty sure I've seen at least one case
where turning it on caused a whole lotta data to disappear.

--
Robert Haas
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