On Thu, Jan 19, 2023 at 2:54 PM Andres Freund <andres@anarazel.de> wrote:
> Yea. Hence my musing about potentially addressing this by choosing to visit
> additional blocks during the heap scan using vacuum's block sampling logic.
I'd rather just invent a way for vacuumlazy.c to tell the top-level
vacuum.c caller "I didn't update reltuples, but you ought to go
ANALYZE the table now that I'm done, even if you weren't already
planning to do so". This wouldn't have to happen every time, but it
would happen fairly often.
> IME most of the time in analyze isn't spent doing IO for the sample blocks
> themselves, but CPU time and IO for toasted columns. A trimmed down version
> that just computes relallvisible should be a good bit faster.
I worry about that from a code maintainability point of view. I'm
concerned that it won't be very cut down at all, in the end.
Presumably you'll want to add the same I/O prefetching logic to this
cut-down version, just for example. Since without that there will be
no competition between it and ANALYZE proper. Besides which, isn't it
kinda wasteful to not just do a full ANALYZE? Sure, you can avoid
detoasting overhead that way. But even still.
--
Peter Geoghegan