Re: Free Space Map data structure - Mailing list pgsql-hackers

From Gregory Stark
Subject Re: Free Space Map data structure
Date
Msg-id 87d4p062nw.fsf@oxford.xeocode.com
Whole thread Raw
In response to Free Space Map data structure  (Heikki Linnakangas <heikki@enterprisedb.com>)
List pgsql-hackers
"Heikki Linnakangas" <heikki@enterprisedb.com> writes:

> For example:
>
>     9
>  4     9
> 2 4   0 9

It occurs to me now that this it actually wouldn't be so easy to ripple up
changes due to the amount amount of space *decreasing*. Consider if you reduce
the leaf 9 to an 8. You want to decrease its parent to 8 but first you have to
check that its sibling isn't also 9. Again when you get to the grandparnt you
have to check that the "4" isn't a 9. As long as you're on one page that's
cheap but if it means paging in another page of the FSM that could be
annoying.

--  Gregory Stark EnterpriseDB          http://www.enterprisedb.com Ask me about EnterpriseDB's PostGIS support!


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