Re: INSERT waiting under heavy load

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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