Re: Rewriting Free Space Map

"Tom Lane" <tgl@sss.pgh.pa.us> writes:

> "Heikki Linnakangas" <heikki@enterprisedb.com> writes:
>> My original thought was to have a separate RelFileNode for each of the 
>> maps. That would require no smgr or xlog changes, and not very many 
>> changes in the buffer manager, though I guess you'd more catalog 
>> changes. You had doubts about that on the previous thread 
>> (http://archives.postgresql.org/pgsql-hackers/2007-11/msg00204.php), but 
>> the "map forks" idea certainly seems much more invasive than that.
>
> The main problems with that are (a) the need to expose every type of map
> in pg_class and (b) the need to pass all those relfilenode numbers down
> to pretty low levels of the system.  The nice thing about the fork idea
> is that you don't need any added info to uniquely identify what relation
> you're working on.  The fork numbers would be hard-wired into whatever
> code needed to know about particular forks.  (Of course, these same
> advantages apply to using special space in an existing file.  I'm
> just suggesting that we can keep these advantages without buying into
> the restrictions that special space would have.)

One advantage of using separate relfilenodes would be that if we need to
regenerate a map we could do it in a new relfilenode and swap it in like we do
with heap rewrites.

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