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

On Mon, Jul 01, 2024 at 03:58:16PM -0400, Robert Haas wrote:
> On Mon, Jul 1, 2024 at 3:47 PM Nathan Bossart <nathandbossart(at)gmail(dot)com> wrote:
>> 0001 introduces a new API for registering callbacks and running them in
>> parallel on all databases in the cluster. This new system manages a set of
>> "slots" that follow a simple state machine to asynchronously establish a
>> connection and run the queries. It uses system() to wait for these
>> asynchronous tasks to complete. Users of this API only need to provide two
>> callbacks: one to return the query that should be run on each database and
>> another to process the results of that query. If multiple queries are
>> required for each database, users can provide multiple sets of callbacks.
>
> I do really like the idea of using asynchronous communication here. It
> should be significantly cheaper than using multiple processes or
> threads, and maybe less code, too. But I'm confused about why you
> would need or want to use system() to wait for asynchronous tasks to
> complete. Wouldn't it be something like select()?

Whoops, I meant to type "select()" there. Sorry for the confusion.

--
nathan