From: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
---|---|
To: | Guillaume Lelarge <guillaume(at)lelarge(dot)info>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Misunderstanding on the FSM README file |
Date: | 2014-12-07 14:07:11 |
Message-ID: | 54845F0F.3000103@vmware.com |
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Lists: | pgsql-hackers |
On 12/07/2014 02:03 PM, Guillaume Lelarge wrote:
> Hi,
>
> I've been reading the FSM README file lately
> (src/backend/storage/freespace/README), and I'm puzzled by one of the graph
> (the binary tree structure of an FSM file). Here it is:
>
> 4
> 4 2
> 3 4 0 2 <- This level represents heap pages
>
> Shouldn't the last line be:
> 4 3 2 0
>
> (ie, highest number of free space on the left node, lowest on the right one)
>
> Probably just nitpicking, but still, I'm wondering if I missed something
> out.
No, that's not how it works. Each number at the bottom level corresponds
to a particular heap page. The first number would be heap page #0 (which
has 3 units of free space), the second heap page #1 (with 4 units of
free space) and so forth. Each node on the upper levels stores the
maximum of its two children.
- Heikki
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