Re: Skip index cleanup if autovacuum did not do any work

On Tue, Nov 28, 2017 at 1:36 PM, Feike Steenbergen
<feikesteenbergen(at)gmail(dot)com> wrote:
> On a server with a very frequent xid wraparound I can see that the
> anti-wraparound vacuum is finished very quickly with the heap, yet it still
> scans all the indexes, which causes it to still have to read a lot of data,
> which takes a considerable amount of time.
>
> I dove into the code a bit and as far as I can tell, all the time spent for
> doing this is is in lazy_cleanup_index.
>
> For the very specific use case of all-frozen, basically read-only tables,
> would it be ok to skip the lazy_cleanup_index call? As we are sure we did
> not touch the heap or the index, I'd say a cleanup may not be necessary.

There is a patch in the ongoing CF to do this:

https://commitfest.postgresql.org/15/952/

It's a lot harder to do this correctly than it first appears.

--
Peter Geoghegan