Oops, pressed send too early. Ignore the one-line reply I just sent...
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.
You can't move tuples around in a page without holding a Vacuum lock on
the page. Some other backend might have the page pinned and have a
pointer to a tuple on the page that would get bogus if the tuple is
moved. Maybe you could try to get a vacuum lock when doing the update
and prereserve space for the new version if you can get one.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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