Re: Rearchitecting for storage

On Thu, 18 Jul 2019 at 19:53, Rob Sargent <robjsargent(at)gmail(dot)com> wrote:

>
> >
> > That would likely keep the extra storage requirements small, but still
> non-zero. Presumably the upgrade would be unnecessary if it could be done
> without rewriting files. Is there any rule of thumb for making sure one
> has enough space available for the upgrade? I suppose that would come
> down to what exactly needs to get rewritten, in what order, etc., but the
> pg_upgrade docs don't seem to have that detail. For example, since we've
> got an ~18TB table (including its indices), if that needs to be rewritten
> then we're still looking at requiring significant extra storage. Recent
> experience suggests postgres won't necessarily do things in the most
> storage-efficient way.. we just had a reindex on that database fail (in
> --single-user) because 17TB was insufficient free storage for the db to
> grow into.
> >
> Can you afford to drop and re-create those 6 indices?

Technically, yes. I don't see any reason we'd be prevented from doing
that. But, rebuilding them will take a long time. That's a lot of
downtime to incur any time we update the DB. I'd prefer to avoid it if I
can. For scale, the recent 'reindex database' that failed ran for nine
days before it ran out of room, and that was in single-user. Trying to do
that concurrently would take a lot longer, I imagine.