Обсуждение: Misunderstanding on the FSM README file
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
4 3 2 0
(ie, highest number of free space on the left node, lowest on the right one)
Thanks.
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
2014-12-07 15:07 GMT+01:00 Heikki Linnakangas <hlinnakangas@vmware.com>:
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.
Oh OK. Thanks Heikki, that makes perfect sense.
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