Re: [HACKERS] Support for pg_receivexlog --format=plain|tar

On Fri, Jan 6, 2017 at 11:07 PM, Magnus Hagander <magnus@hagander.net> wrote:
> A few further notes:

Thanks for the review.

> You are using the filemode to gzopen and the mode_compression variable to
> set the compression level. The pre-existing code in pg_basebackup uses
> gzsetparams(). Is there a particular reason you didn't do it the same way?
>
> Small comment:
> -   if (pad_to_size)
> +   if (pad_to_size && dir_data->compression == 0)
>     {
>         /* Always pre-pad on regular files */
>
>
> That "always" is not true anymore. Commit-time cleanup can be done of that.
>
> The rest of this looks good to me, but please comment on the gzopen part
> before we proceed to commit :)

Yes using gzsetparams() looks cleaner. I actually thought about using
the same logic as pg_dump. Attached is an updated patch.

There is something I forgot. With this patch,
FindStreamingStart()@pg_receivexlog.c is actually broken. In short it
forgets to consider files that have been compressed at the last run of
pg_receivexlog and will try to stream changes from the beginning. I
can see that gzip -l provides this information... But I have yet to
find something in zlib that allows a cheap lookup as startup of
streaming should be fast. Looking at how gzip -l does it may be faster
than looking at the docs.