On Fri, Jan 06, 2006 at 04:49:09PM -0500, Tom Lane wrote:
> performance risk in the sort of scenario you are describing.
> (I'm not sure why it would manifest as transactions showing "INSERT
> waiting" state though.)
It's because of I/O. When you have a large number of updates, the
planner always assumes an indexscan (correctly), but you end up
scanning megabytes of dead tuples. With a large number of open
transactions, most of the time VACUUM can't recover the space. I
agree with what Tom said earlier in this thread: the design is
guaranteed to lose.
A
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