Heikki Linnakangas wrote:
> On 30.11.2010 18:33, Tom Lane wrote:
> > Robert Haas<robertmhaas(at)gmail(dot)com> writes:
> >> Oh, but it's worse than that. When you XLOG a WAL record for each of
> >> those pages, you're going to trigger full-page writes for all of them.
> >> So now you've turned 1GB of data to write into 2+ GB of data to
> >> write.
> > No, because only the first mod of each VM page would trigger a full page
> > write, at least assuming a reasonable ordering of the operations.
> If you change the LSN on the heap pages, you have to write full page
> images of those as well.
> Let's recap what happens when a VM bit is set: You set the
> PD_ALL_VISIBLE flag on the heap page (assuming it's not set already, it
> usually isn't), and then set the bit in the VM while keeping the heap
> page locked.
What if we set PD_ALL_VISIBLE on the heap page, wait for a checkpoint to
happen so the heap page is guaranteed to be on disk, then on next read,
if PD_ALL_VISIBLE is set and the VM all-visible bit is not set, set the
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
+ It's impossible for everything to be true. +
In response to
pgsql-hackers by date
|Next:||From: Bruce Momjian||Date: 2010-12-01 01:57:56|
|Subject: Re: DELETE with LIMIT (or my first hack)|
|Previous:||From: Jeff Janes||Date: 2010-11-30 22:56:46|
|Subject: Re: Spread checkpoint sync|