Re: pg_stat_progress_basebackup - progress reporting forpg_basebackup, in the server side - Mailing list pgsql-hackers

On 2020/03/11 3:39, Magnus Hagander wrote:
> On Tue, Mar 10, 2020 at 6:19 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>>
>>
>>
>> On 2020/03/10 22:43, Amit Langote wrote:
>>> On Tue, Mar 10, 2020 at 6:09 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>>>>> So, I will make the patch adding support for --no-estimate-size option
>>>>> in pg_basebackup.
>>>>
>>>> Patch attached.
>>>
>>> Like the idea and the patch looks mostly good.
>>
>> Thanks for reviewing the patch!
>>
>>> +      total size. If the estimation is disabled in
>>> +      <application>pg_basebackup</application>
>>> +      (i.e., <literal>--no-estimate-size</literal> option is specified),
>>> +      this is always <literal>0</literal>.
>>>
>>> "always" seems unnecessary.
>>
>> Fixed.
>>
>>> +        This option prevents the server from estimating the total
>>> +        amount of backup data that will be streamed. In other words,
>>> +        <literal>backup_total</literal> column in the
>>> +        <structname>pg_stat_progress_basebackup</structname>
>>> +        view always indicates <literal>0</literal> if this option is enabled.
>>>
>>> Here too.
>>
>> Fixed.
>>
>> Attached is the updated version of the patch.
> 
> Would it perhaps be better to return NULL instead of 0 in the
> statistics view if there is no data?
> 
> Also, should it really  be the server version that decides how this
> feature behaves, and not the pg_basebackup version? Given that the
> implementation is entirely in the client, it seems that's more
> logical?

Yeah, you're right. I changed the patch that way.
Attached is the updated version of the patch.
  
> and a few docs nitpicks:
> 
>          <para>
>           Whether this is enabled or not, the
>           <structname>pg_stat_progress_basebackup</structname> view
> -        report the progress of the backup in the server side. But note
> -        that the total amount of data that will be streamed is estimated
> -        and reported only when this option is enabled. In other words,
> -        <literal>backup_total</literal> column in the view always
> -        indicates <literal>0</literal> if this option is disabled.
> +        report the progress of the backup in the server side.
> +       </para>
> +       <para>
> +        This option is not allowed when using
> +        <option>--no-estimate-size</option>.
>          </para>
> 
> I think you should just remove that whole paragraph. The details are
> now listed under the disable parameter.

Fixed.

> +        This option prevents the server from estimating the total
> +        amount of backup data that will be streamed. In other words,
> +        <literal>backup_total</literal> column in the
> +        <structname>pg_stat_progress_basebackup</structname>
> +        view indicates <literal>0</literal> if this option is enabled.
> 
> I suggest just "This option prevents the server from estimating the
> total amount of backup data that will be streamed, resulting in the
> ackup_total column in pg_stat_progress_basebackup to be (zero or NULL
> depending on above)".
> 
> (Markup needed on that of course ,but you get the idea)

Yes, fixed.

> +        When this is disabled, the backup will start by enumerating
> 
> I'd try to avoid the double negation, with something "without this
> parameter, the backup will start..."

Fixed. I used "Without using this option ...".
  
> +  <para>
> +   <application>pg_basebackup</application> asks the server to estimate
> +   the total amount of data that will be streamed by default (unless
> +   <option>--no-estimate-size</option> is specified) in version 13 or later,
> +   and does that only when <option>--progress</option> is specified in
> +   the older versions.
> +  </para>
> 
> That's an item for the release notes, not for the reference page, I
> think. It's already explained under the --disable parameter, so I
> suggest removing this paragraph as well.

Fixed.

Regards,

-- 
Fujii Masao
NTT DATA CORPORATION
Advanced Platform Technology Group
Research and Development Headquarters