Re: Attempt to consolidate reading of XLOG page

On 2019-Nov-22, Michael Paquier wrote:

> On Fri, Nov 22, 2019 at 10:35:51AM -0300, Alvaro Herrera wrote:
> > FWIW I think the new code is buggy because it doesn't seem to be setting
> > ws_off, so I suppose the optimization in ReadPageInternal to skip
> > reading the page when it's already the page we have is not hit, except
> > for the first page in the segment. I didn't verify this, just my
> > impression while reading the code.
>
> FWIW, this matches with my impression here, third paragraph:
> https://www.postgresql.org/message-id/20191120083802.GB47145@paquier.xyz

Ah, right.

I was wondering if we shouldn't do away with the concept of "offset" as
such, since the offset there is always forcibly set to the start of a
page. Why don't we count page numbers instead? It seems like the
interface is confusingly generic (measure in bytes) yet not offer any
extra functionality that could not be obtained with a simpler struct
repr (measure in pages).

But then that's not something that we need to change in this patch.

--
Álvaro Herrera https://www.2ndQuadrant.com/
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