Re: optimizing pg_upgrade's once-in-each-database steps

On Wed, Sep 04, 2024 at 12:28:23AM +0100, Ilya Gladyshev wrote:
> The fix looks right to me, but I got confused by the skip_wait and this
> `if`:
>
> +            if (PQstatus(slot->conn) != CONNECTION_OK)
> +                return;
>
> This branch checks connection status that hasn't been refreshed after the
> select. When we go back to wait_slots after this, PQconnectPoll will refresh
> the connection status and run select with skip_wait=true, I believe, we
> could simplify this by moving the PQconnectPoll back to the process_slots,
> so that we can process connection right after polling, if it's ready.

Ah, yes, that's a nice way to simplify things. I ended up just making it
process_slot()'s responsibility to set the correct select_mode, at which
point the logic in the switch statement in wait_on_slots() is sparse enough
that it seems better to convert it to a couple of short "if" statements.

--
nathan