I was actually thinking that we could slip this in 8.3. It's a simple, well-understood patch, which fixes a little data integrity quirk as well as gives a nice recovery speed up.

Bruce Momjian wrote:
I assume this is 8.4 material.


Heikki Linnakangas wrote:
Tom Lane wrote:
"Simon Riggs" <[EMAIL PROTECTED]> writes:
As regards the zero_damaged_pages question, I raised that some time ago
but we didn't arrive at an explicit answer. All I would say is we can't
allow invalid pages in the buffer manager at any time, whatever options
we have requested, otherwise other code will fail almost immediately.
Yeah --- the proposed new bufmgr routine should probably explicitly zero
the content of the buffer.  It doesn't really matter in the context of
WAL recovery, since there can't be any concurrent access to the buffer,
but it'd make it safe to use in non-WAL contexts (I think there are
other places where we know we are going to init the page and so a
physical read is a waste of time).
To implement that correctly, I think we'd need to take the content lock to clear the buffer if it's already found in the cache. It doesn't seem right to me for the buffer manager to do that, in the worst case it could lead to deadlocks if that function was ever used while holding another buffer locked.

What we could have is the semantics of "Return a buffer, with either correct contents or completely zeroed out". It would act just like ReadBuffer if the buffer was already in memory, and zero out the page otherwise. That's a bit strange semantics to have, but is simple to implement and works for the use-cases we've been talking about.

Patch implementing that attached. I named the function "ReadOrZeroBuffer".

   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend

  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

---------------------------(end of broadcast)---------------------------
TIP 7: You can help support the PostgreSQL project by donating at


Reply via email to