Re: Block write statistics WIP

On 5/20/13 7:51 AM, Heikki Linnakangas wrote:
>> The way that MarkDirty requires this specific underlying storage manager
>> behavior to work properly strikes me as as a bit of a layering violation
>> too. I'd like the read and write paths to have a similar API, but here
>> they don't even operate on the same type of inputs. Addressing that is
>> probably harder than just throwing a hack on the existing code though.
>
> To be honest, I don't understand what you mean by that. ?

Let's say you were designing a storage layer API from scratch for what 
Postgres does.  That might take a relation as its input, like ReadBuffer 
does.  Hiding the details of how that turns into a physical file 
operation would be a useful goal of such a layer.  I'd then consider it 
a problem if that exposed things like the actual mapping of relations 
into files to callers.

What we actually have right now is this MarkDirty function that operates 
on BufferTag data, which points directly to the underlying file.  I see 
that as cutting the storage API in half and calling a function in the 
middle of the implementation.  It strikes me as kind of weird that the 
read side and write side are not more symmetrical.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
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