Re: heap vacuum & cleanup locks

On Fri, Nov 4, 2011 at 6:18 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> Here's a new version.  I fixed the second pass as discussed (which
> turned out to be trivial).  To address the concern about relpages, I
> moved this pre-existing line to after we get the buffer lock:
>
> +               vacrelstats->scanned_pages++;
>
> That appears to do the right thing.

I think we need to count skipped pages also. I don't like the idea
that vacuum would just report less pages than there are in the table.
We'll just get requests to explain that.

> I found it kind of confusing that lazy_scan_page_for_wraparound()
> returns with the pin either held or not held depending on the return
> value, so I rearranged things very slightly so that it doesn't need to
> do that.  I'm wondering whether we should rename that function to
> something like lazy_check_needs_freeze().

OK

> I tested this out and discovered that "VACUUM FREEZE" doesn't set the
> for_wraparound flag.  On further review, I think that we should
> probably conditionalize the behavior on the scan_all flag that
> lazy_vacuum_rel sets, rather than for_wraparound.  Otherwise, there's
> no way for the user to manually force relfrozenxid to advance, which
> doesn't seem good.  I haven't made that change in this version,
> though.

Agreed, separate patch.

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