On Thu, 18 Jul 2019 at 19:53, Rob Sargent <robjsarg...@gmail.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.
