| From: | Gregory Stark <stark(at)enterprisedb(dot)com> |
|---|---|
| To: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> |
| Cc: | "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Free Space Map data structure |
| Date: | 2008-04-08 10:50:43 |
| Message-ID: | 87d4p062nw.fsf@oxford.xeocode.com |
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| Lists: | pgsql-hackers |
"Heikki Linnakangas" <heikki(at)enterprisedb(dot)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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