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    g...@2ndquadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com

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