Re: Patch to improve reliability of postgresql on linux nfs

On Tue, Sep 13, 2011 at 10:14 AM, Florian Pflug <fgp@phlo.org> wrote:

>> Personally, I'ld think that's ripe for bugs.   If the contract is that
>> ret != amount is the "error" case, then don't return -1 for an error
>> *sometimes*.
>
> Hm, but isn't that how write() works also? AFAIK (non-interruptible) write()
> will return the number of bytes written, which may be less than the requested
> number if there's not enough free space, or -1 in case of an error like
> an invalid fd being passed.

Looking through the code, it appears as if all the write calls I've
seen are checking ret != amount, so it's probably not as big a deal
for PG as I fear...

But the subtle change in semantics (from system write ret != amount
not necessarily a real error, hence no errno set) of pg_write ret !=
amount only happening after a "real error" (errno should be set) is
one that could yet lead to confusion.

a.


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