Holger Hoffstaette wrote:
Hi -
I have been following this thread and find some of the recommendations
really surprising. I understand that MVCC necessarily creates overhead,
in-place updates would not be safe against crashes etc. but have a hard
time believing that this is such a huge problem for RDBMS in 2008. How do
large databases treat mass updates? AFAIK both DB2 and Oracle use MVCC
(maybe a different kind?) as well, but I cannot believe that large updates
still pose such big problems.
Are there no options (algorithms) for adaptively choosing different
update strategies that do not incur the full MVCC overhead?
I think Pg already does in place updates, or close, if the tuples being
replaced aren't referenced by any in-flight transaction. I noticed a
while ago that if I'm doing bulk load/update work, if there aren't any
other transactions no MVCC bloat seems to occur and updates are faster.
I'd be interested to have this confirmed, as I don't think I've seen it
documented anywhere. Is it a side-effect/benefit of HOT somehow?
--
Craig Ringer
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