Re: [PROPOSAL] VACUUM Progress Checker.

On 2015/12/10 4:40, Robert Haas wrote:
> It's going to be *really* important that this facility provides a
> lightweight way of updating progress, so I think this whole API is
> badly designed.  VACUUM, for example, is going to want a way to update
> the individual counter for the number of pages it's scanned after
> every page.  It should not have to pass all of the other information
> that is part of a complete report.  It should just be able to say
> pgstat_report_progress_update_counter(1, pages_scanned) or something
> of this sort.  Don't marshal all of the data and then make
> pgstat_report_progress figure out what's changed.  Provide a series of
> narrow APIs where the caller tells you exactly what they want to
> update, and you update only that.  It's fine to have a
> pgstat_report_progress() function to update everything at once, for
> the use at the beginning of a command, but the incremental updates
> within the command should do something lighter-weight.

How about something like the following:

/** index: in the array of uint32 counters in the beentry* counter: new value of the (index+1)th counter*/
void pgstat_report_progress_update_counter(int index, uint32 counter);

/** msg: new value of (index+1)the message (with trailing null byte)*/
void pgstat_report_progress_update_message(int index, const char *msg);

Actually updating a counter or message would look like:

pgstat_increment_changecount_before(beentry);
// update the counter or message at index in beentry->st_progress_*
pgstat_increment_changecount_after(beentry);

Other interface functions which are called at the beginning:

void pgstat_report_progress_set_command(int commandId);
void pgstat_report_progress_set_command_target(const char *target_name);
or
void pgstat_report_progress_set_command_target(Oid target_oid);

And then a SQL-level,
void pgstat_reset_local_progress();

Which simply sets beentry->st_command to some invalid value which signals
a progress view function to ignore this backend.

Thanks,
Amit