On Aug 17, 2006, at 4:10 PM, Martijn van Oosterhout wrote:
On Thu, Aug 17, 2006 at 02:54:20PM -0500, Jim C. Nasby wrote:
On Thu, Aug 17, 2006 at 02:23:48PM +0200, Martijn van Oosterhout wrote:
On Thu, Aug 17, 2006 at 12:55:28PM +0900, ITAGAKI Takahiro wrote:
But the method has the above problem. So I suggest to use whether
the right link points to the next adjacent page or not.

if (opaque->btpo_next != P_NONE && opaque->btpo_next != blkno + 1)

Do you think which method is better? Or do you have other ideas?

Ok, fine... expand the example out to an index that's not trivial in
size. Even with read-ahead, once you get to a few megs (which is
obviously not that big), you're seeking.

Well, mostly I'm just saying that only matching on the next block
number is going to give unrealistically low numbers. We can't ignore OS
level caching, the way Postgres works relies on it in many ways.

While I agree that *users* must take caching into account, I don't think we should be fudging fragmentation numbers. For starters, we have absolutely no idea how much caching is actually happening.

We should just report the raw numbers and let users draw their own conclusions. Doing otherwise makes the stat far less useful.
Jim C. Nasby, Sr. Engineering Consultant      [EMAIL PROTECTED]
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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