Re: pg_stat_progress_basebackup - progress reporting forpg_basebackup, in the server side

On 2020/03/19 1:22, Magnus Hagander wrote:
> On Wed, Mar 18, 2020 at 5:14 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>>
>>
>>
>> On 2020/03/19 0:37, Magnus Hagander wrote:
>>> On Wed, Mar 11, 2020 at 5:53 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>>>>
>>>>
>>>>
>>>> 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?
>>>
>>> Did you miss this comment, or not agree? :)
>>
>> Oh, I forgot to attached the patch... Patch attached.
>> This patch needs to be applied after applying
>> add_no_estimate_size_v3.patch.
> 
> :)
> 
> Hmm. I'm slightly irked by doing the -1 -> NULL conversion in the SQL
> view.  I wonder if it might be worth teaching
> pg_stat_get_progress_info() about returning NULL?

That's possible by
- adding the boolean array like st_progress_null[PGSTAT_NUM_PROGRESS_PARAM]
    that indicates whether each column is NULL or not, into PgBackendStatus
- extending pgstat_progress_update_param() and pgstat_progress_update_multi_param()
    so that they can update the boolean array for NULL
- updating the progress reporting code so that the extended versions of
    function are used

I didn't adopt this idea because it looks a bit overkill for the purpose.
OTOH, this would be good improvement for the progress reporting
infrastructure and I'm fine to implement it.

Regards,

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