Simon Riggs wrote:
On Thu, 2006-11-09 at 18:28 -0500, Tom Lane wrote:
"Simon Riggs" <[EMAIL PROTECTED]> writes:
HOT can only work in cases where a tuple does not modify one of the
columns defined in an index on the table, and when we do not alter the
row length of the tuple.
Seems like "altering the row length" isn't the issue, it's just "is
there room on the page for the new version". Again, a generous
fillfactor would give you more flexibility.
The copy-back operation can only work if the tuple fits in the same
space as the root tuple. If it doesn't you end up with a tuple
permanently in the overflow relation. That might not worry us, I guess.
Also, my understanding was that an overwrite operation could not vary
the length of a tuple (at least according to code comments).
You can't If someone else has the page pinned,
[We'll be able to do that more efficiently when
we have plan invalidation]
Uh, what's that got to do with it?
Currently the HOT code dynamically tests to see if the index columns
have been touched. If we had plan invalidation that would be able to be
assessed more easily at planning time, in cases where there is no BEFORE
trigger.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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