Re: [HACKERS] LONG

> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > There are so many mails for me to follow about this issue. 
> > For example,what's the conclusion about the following ?
> 
> I don't think it's concluded yet...
> 
> > Why is CTID needed ?  Is it necessary to know "primary" tuples from
> > out-of-lines values ? 
> 
> It seems to me that the primary tuple should store CTIDs of the
> out-of-line segment(s) it's using.  That way, we need no index at
> all on the expansion relation, which would clearly be a win.

That could be bad.  Vacuum moving expired entries in long_ tables would
need to update the ctids in the primary relation, which would be a mess.
Also, I can see an 16MB relation using 8k of stored ctids.  Entries over
16MB would be overflow, causing problems.  I think an index and
tradition access will be just fine.

> 
> My thought was that if the expansion tuples stored CTIDs of their
> primary tuples, then it would be practical to have VACUUM consult
> the primary tuples' xact status while vacuuming the expansion.
> That way, we'd have no need to update expansion tuples when changing
> xact status of primary tuples.  But I think Jan has something else
> in mind for that.

Then you need to have a way to point back to the primary table from the
long_ table.  Doesn't seem worth it.

Also, I am questioning the use of compressed for long tuples.  I often
don't want some compression happening behind the scenes.

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