Re: [PATCHES] VACUUM Improvements - WIP Patch

Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> I like the idea of only having to do a single pass through the table though.

Well, that argument was already overstated: we're not re-reading all of
the table now. Just the pages containing dead line pointers.

> Couldn't Pavan's original plan still work and just not have other clients try
> to remove dead line pointers?

You could simply delay recycling of the really-truly-dead line pointers
until the next VACUUM, I suppose. It's not clear how bad a
line-pointer-bloat problem that might leave you with. (It would still
require tracking whether the last vacuum had completed successfully.
I note that any simple approach to that would foreclose ever doing
partial-table vacuums, which is something I thought was on the table
as soon as we had dead space mapping ability.)

> At least not unless they're also pruning the
> page due to an insert or update anyways?

Please stop pretending that this overhead will only be paid by
insert/update. The current design for pruning does not work that way,
and we do not have a better design available.

regards, tom lane