Re: VACUUM touching file but not updating relation

Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> On Fri, Nov 18, 2011 at 2:47 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Well, it's expected given the current coding in the btree vacuum logic.
>> It's not clear to me why it was written like that, though.

> The code works as designed.

> _bt_delitems_vacuum() is only ever called with nitems == 0 when it is
> the last block of the relation with wal_level = hot standby

> As discussed in the comments we must issue a WAL record for the last
> block, whatever else has occurred.

> So the correct number of WAL records is emitted and I see no bug there.

What Thom's complaining about is that the buffer may be marked dirty
unnecessarily, ie when there has been no actual data change.

regards, tom lane