On Tue, Jan 17, 2006 at 03:05:29PM +0100, Michael Riess wrote:
> There must be a way to implement a daemon which frees up space of a
> relation without blocking it too long.
Define "too long". If I have a table that needs to respond to a
SELECT in 50ms, I don't have time for you to lock my table. If this
were such an easy thing to do, don't you think the folks who came up
wit the ingenious lazy vacuum system would have done it?
Remember, a vacuum full must completely lock the table, because it is
physically moving bits around on the disk. So a SELECT can't happen
at the same time, because the bits might move out from under the
SELECT while it's running. Concurrency is hard, and race conditions
are easy, to implement.
A
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Andrew Sullivan | ajs@crankycanuck.ca
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