Alvaro Herrera wrote:
Greg Smith escribió:
On Thu, 15 May 2008, Pavan Deolasee wrote:
I had suggested in the past that whenever we set hint bits for a tuple,
we should check all other tuples in the page and set their hint bits
too to avoid multiple writes of the same page. I guess the idea got
rejected because of lack of benchmarks to prove the benefit.
From glancing at http://www.postgresql.org/docs/faqs.TODO.html I got the
impression the idea was to have the background writer get involved to
help with this particular situation.
The problem is that the bgwriter does not understand about the content
of the pages it is writing -- they're opaque pages for all it knows. So
it cannot touch the hint bits.
We know what kind of a relation we're dealing with in ReadBuffer, so we
could add a flag to BufferDesc to mark heap pages.
If we had the bitmask in a separate map fork, this could be cheap.
I don't buy that. The point of a hint bit is that it's right there along
with the tuple you're looking at. If you have to look at a separate
buffer, you might as well just look at clog.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
