Re: Reliable WAL file shipping over unreliable network

Really? I think you really need to think about it.  You are dealing with a race condition.

While your though process might seem to work and it will appear to work; however in the end it will fail — like I said;
I’veseen it fail first hand. 

You are dealing with a race condition involving filesystem metadata.  If you choose to not use “-c” option then; all I
cantell you is that you have been warned. 


> On Feb 28, 2018, at 1:26 PM, Dianne Skoll <dfs@roaringpenguin.com> wrote:
>
> On Wed, 28 Feb 2018 13:15:48 -0500
> Rui DeSousa <rui.desousa@icloud.com> wrote:
>
>> Sure it does… what happens if the archive server gets full? There is
>> a situation that can fool rsync into thinking it was successfully
>> transferred as rsync only relies on filesystem metadata to verify the
>> file is different.
>
> That's incorrect.  The original transfer will fail and rsync will remove
> the temporary file.  It doesn't rename the file to the final destination
> until and unless the transfer is successful.
>
> "-c" is only used for files that might change multiple times per second;
> since most file systems have only 1-second granualarity in file timestamps,
> you can't rely on a file being identical if the size and timestamps are the
> same.
>
>> The “-c” option will validate the file using a checksum and not just
>> rely on just filesystem metadata.
>
> That's incorrect.  "-c" applies only when rsync looks at existing files
> to see if they differ.  It does not affect what happens when rsync actually
> copies the file data over; that's always verified with a checksum.
>
> Regards,
>
> Dianne.
>