Re: Implement waiting for wal lsn replay: reloaded

On Fri, Feb 28, 2025 at 3:55 PM Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru> wrote:
> 28.02.2025 16:03, Yura Sokolov пишет:
> > 17.02.2025 00:27, Alexander Korotkov wrote:
> >> On Thu, Feb 6, 2025 at 10:31 AM Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru> wrote:
> >>> I briefly looked into patch and have couple of minor remarks:
> >>>
> >>> 1. I don't like `palloc` in the `WaitLSNWakeup`. I believe it wont issue
> >>> problems, but still don't like it. I'd prefer to see local fixed array, say
> >>> of 16 elements, and loop around remaining function body acting in batch of
> >>> 16 wakeups. Doubtfully there will be more than 16 waiting clients often,
> >>> and even then it wont be much heavier than fetching all at once.
> >>
> >> OK, I've refactored this to use static array of 16 size. palloc() is
> >> used only if we don't fit static array.
> >
> > I've rebased patch and:
> > - fixed compiler warning in wait.c ("maybe uninitialized 'result'").
> > - made a loop without call to palloc in WaitLSNWakeup. It is with "goto" to
> > keep indentation, perhaps `do {} while` would be better?
>
> And fixed:
> 'WAIT' is marked as BARE_LABEL in kwlist.h, but it is missing from
> gram.y's bare_label_keyword rule

Thank you, Yura. I've further revised the patch. Mostly added the
documentation including SQL command reference and few paragraphs in
the high availability chapter explaining the read-your-writes
consistency concept.

------
Regards,
Alexander Korotkov
Supabase