From: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
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To: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Free space management within heap page |
Date: | 2007-01-23 09:37:30 |
Message-ID: | 45B5D75A.5040003@enterprisedb.com |
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Lists: | pgsql-hackers |
Pavan Deolasee wrote:
> I am thinking that maintaining fragmented free space within a heap page
> might be a good idea. It would help us to reuse the free space ASAP without
> waiting for a vacuum run on the page. This in turn will lead to lesser heap
> bloats and also increase the probability of placing updated tuple in the
> same heap page as the original one.
Agreed.
> So during a sequential or index scan, if a tuple is found to be dead, the
> corresponding line pointer is marked "unused" and the space is returned
> to a
> free list. This free list is maintained within the page. A linked-list can
> be used for this purpose and the special area of the heap-page can be used
> to track the fragment list. We can maintain some additional information
> about the fragmented space such as, total_free_space, max_fragment_size,
> num_of_fragments etc in the special area.
Maintaining a list like that seems like a lot of hassle to me. Instead,
you could just scan the line pointers looking for a dead tuple of the
right size. We already have to scan the line pointers when inserting to
find a free line pointer.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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