Re: Lock-free compaction. Why not?

On Wed, 10 Jul 2024 at 22:58, Tomas Vondra
<tomas.vondra@enterprisedb.com> wrote:
> IIRC long time ago VACUUM FULL actually worked in a similar way, i.e. by
> moving rows around. I'm not sure if it did the lock-free thing as
> proposed here (probably not), but I guess at least some of the reasons
> why it was replaced by CLUSTER would still apply to this new thing.

Yeah, that changed in 9.0.  The old version still obtained an AEL on the table.

I think the primary issue with the old way was index bloat wasn't
fixed. The release notes for 9.0 do claim the CLUSTER method "is
substantially faster in most cases", however, I imagine there are
plenty of cases where it wouldn't be. e.g, it's hard to imagine
rewriting the entire 1TB table and indexes is cheaper than moving 1
row out of place row.

David