Re: [PROPOSAL] VACUUM Progress Checker.

Hi,

Thanks for taking a look at the patch.

On Mon, Mar 14, 2016 at 6:55 PM, Rahila Syed <rahilasyed90(at)gmail(dot)com> wrote:
> Hello,
>
> While I am still looking at this WIP patch, I had one suggestion.
>
> Instead of making changes in the index AM API can we have a call to update
> the shared state using pgstat_progress* API
>
> directly from specific index level code?
>
> Like pgstat_count_index_scan(rel) call from _bt_first does. Though this
> function basically updates local structures and sends the count to stat
> collector via messages we can have a function which will instead modify the
> shared state using the progress API committed recently.

I chose the callback approach because we need to count the index
blocks within the context of a given vacuum run. For example, as
proposed, progress_callback_state (in this case, a pointer to the
LVRelStats struct for a given vacuum run) keeps the block count for a
given index vacuum run. It is reset when next index vacuuming round
starts. Also, remember that the count is across all indexes.

If we call pgstat_progress API directly from within AM, what I just
described above seems difficult to achieve modularly. But maybe, I'm
missing something.

Aside from whether we should use one of the above two methods, I think
we also have to figure out, for each AM, how to count correctly
considering non-linearity (tree traversal, recursion and such) of most
AMs' vacuum scans.

Thanks,
Amit