On Fri, Jan 28, 2011 at 10:13 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> I was thinking about full-page writes again tonight. I'm still
>> wondering about the feasibility of getting rid of full-page writes for
>> certain operations. We can do this, I think, in any case where we can
>> convince ourselves that if the original operation, or a redo of the
>> original operation, leaves behind a torn page, a subsequent redo will
>> still DTRT.
>
>> I think that both tuple freezing (XLOG_HEAP2_FREEZE) and heap
>> deletions (XLOG_HEAP_DELETE) are close to having this property.
>
> Say what? A heap deletion compacts the page --- it will certainly fail
> badly on torn-page.
What do you mean by "compacts the page"? I would interpret that to
mean "reclaims the space formerly used by the tuple being deleted",
but it certainly can't do that. The transaction might not commit, and
in any case the tuple will still be visible to concurrent snapshots.
--
Robert Haas
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