On Fri, 6 Apr 2007, Takayuki Tsunakawa wrote:
Hmm... what makes you think that sync writes is useful for Oracle and
not for PostgreSQL?
They do more to push checkpoint-time work in advance, batch writes up more
efficiently, and never let clients do the writing. All of which make for
a different type of checkpoint.
Like Simon points out, even if it were conceivable to mimic their design
it might not even be legally feasible. The point I was trying to make is
this: you've been saying that Oracle's writing technology has better
performance in this area, which is probably true, and suggesting the cause
of that was their using O_SYNC writes. I wanted to believe that and even
tested out a prototype. The reality here appears to be that their
checkpoints go smoother *despite* using the slower sync writes because
they're built their design around the limitations of that write method.
I suspect it would take a similar scale of redesign to move Postgres in
that direction; the issues you identified (the same ones I ran into) are
not so easy to resolve. You're certainly not going to move anybody in
that direction by throwing a random comment into a discussion on the
patches list about a feature useful *right now* in this area.
* Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD
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