On Thu, Jul 18, 2019 at 10:09 PM Matthew Pounsett <m...@conundrum.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. >
I've done a test on a virtual machine of mine, with the following three databases: one 0f 4.9 GB, one of 500 MB, one of 50 MB. I know this is not even close to your environment, however upgrading with pg_upgrade from 10.9 to 11.4 _without_ the link option ask for 85% of space. On a machine with a single database of 8.9 GB and a space occupation, as reported by df, of 64% (mean 46% available) I was able to upgrade from 10.9 to 11.4 without the link option. Space occupation increased of 90%. Using the link option on the same cluster required 1.1% of extra space (around 100 MB). Of course, these are poor-man results, but give you an advice on the space required by pg_ugprade (which seems to be less than 100% or 2x). Hope this helps. Luca
