Re: read() returns ERANGE in Mac OS X

Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, May 21, 2012 at 12:23 PM, Tom Lane <tgl@sss.pgh.pa.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.
        regards, tom lane