Re: heap metapages

On Mon, May 21, 2012 at 3:15 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> * Robert Haas (robertmhaas(at)gmail(dot)com) wrote:
>> The FSM and VM are small enough
>> that interleaving them with the actual data probably wouldn't slow
>> down seq scans materially.
>
> Wouldn't that end up potentially causing lots of random i/o if you need
> to look at many parts of the FSM or VM..?

I doubt it. They probably stay in core anyway.

> Also, wouldn't having it at the start of the heap reduce the changes
> needed to the SM?  Along with make such things easier to find
> themselves, when talking about forensics?

The metapage, surely yes. If we wanted to fold the FSM and VM into
the main fork in their entirety, probably not. But I don't have much
desire to do that. I think it's fine for a BIG relation to eat a
couple of inodes. I just don't want a little one to do that.

> Of course, the real challenge here is dealing with such an on-disk
> format change...  If we were starting from scratch, I doubt there would
> be much resistance, but figuring out how to do this and still support
> pg_upgrade could be quite ugly.

That does seem to be the ten million dollar question, but already
we've batted around a few solutions on this thread, so I suspect we'll
find a way to make it work. I think my next step is going to be to
spend some more time studying what the various index AMs already have
in terms of metapages.

--
Robert Haas
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