Re: Free space management within heap page

On Wed, Jan 24, 2007 at 12:45:53PM +0530, Pavan Deolasee wrote:
> My apologies if this has been discussed before. I went through the earlier
> discussions, but its still very fuzzy to me. I am not able to construct a
> case
> where a tuple is DEAD (not RECENTLY_DEAD) and still there could be
> a transaction need to follow the ctid pointer chain from its parent. Can
> somebody help me to construct this scenario ?

I thought the classical example was a transaction that updated the same
tuple multiple times before committing. Then the version prior to the
transaction start isn't dead yet, but all but one of the versions
created by the transaction will be dead (they were never visible by
anybody else anyway).

I beleive other such corner cases are transactions that have
subtransactions that aborted after updating.

But I'm not that knowledgable on MVCC to be sure about that.

Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.