Re: pg_stat_progress_basebackup - progress reporting for pg_basebackup, in the server side

On 2020/03/19 12:02, Amit Langote wrote:
> On Thu, Mar 19, 2020 at 11:45 AM Fujii Masao
> <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote:
>> On 2020/03/19 11:32, Amit Langote wrote:
>>> On Thu, Mar 19, 2020 at 11:24 AM Alvaro Herrera
>>> <alvherre(at)2ndquadrant(dot)com> wrote:
>>>> On 2020-Mar-19, Amit Langote wrote:
>>>>
>>>>> Magnus' idea of checking the values in pg_stat_get_progress_info() to
>>>>> determine whether to return NULL seems fine to me.
>>
>> So you think that the latest patch is good enough?
>
> I see that the latest patch modifies pg_stat_progress_basebackup view
> to return NULL, so not exactly. IIUC, Magnus seems to be advocating
> to *centralize* this in pg_stat_get_progress_info(), which all views
> are based on, which means we need to globally define a NULL param
> value, as Alvaro also pointed out.
>
> But...
>
>>>>> We will need to
>>>>> update the documentation of st_progress_param, because it currently
>>>>> says:
>>>>>
>>>>> * ...but the meaning of each element in the
>>>>> * st_progress_param array is command-specific.
>>>>> */
>>>>> ProgressCommandType st_progress_command;
>>>>> Oid st_progress_command_target;
>>>>> int64 st_progress_param[PGSTAT_NUM_PROGRESS_PARAM];
>>>>> } PgBackendStatus;
>>>>>
>>>>> If we are to define -1 in st_progress_param[] as NULL to the users,
>>>>> that must be mentioned here.
>>>>
>>>> Hmm, why -1? It seems like a value that we might want to use for other
>>>> purposes in other params. Maybe INT64_MIN is a better choice?
>>>
>>> Yes, maybe.
>>
>> I don't think that we need to define the specific value like -1 as NULL globally.
>> Which value should be used for that purpose may vary by each command. Only for
>> pg_stat_progress_basebackup.backup_total, IMO using -1 as special value for
>> NULL is not so bad idea.
>
> This is the first instance of needing to display NULL in a progress
> view, so a non-general solution may be enough for now. IOW, your
> latest patch is good enough for that. :)

Ok, so barring any objection, I will commit the latest patch.

Regards,

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