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.
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