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Re: Join Two Extremely Large Tables

From: Bass Chorng <bchorng_at_yahoo.com>
Date: 17 Apr 2003 12:13:42 -0700
Message-ID: <bd9a9a76.0304171113.c96a23a@posting.google.com>


Connor McDonald <connor_mcdonald_at_yahoo.com> wrote in message news:<3E9E39BF.6878_at_yahoo.com>...
> > Your advice is appreciated.
>
> Hash joins are very senstive to the quality in the optimizer stats. As
> a result, the main drama you might encounter with hash joins is that
> they tend to go exponentially bad when you run out of memory, you end up
> with massive amounts of temp space used, and re-used, and re-used.
>

  Yup, that's exactly what my concern is. I think hash join behaves   like sort - when you are out of memory, it does not "continue"   the operation to temp segment. It stops and copies the entire   momory to disk. This is worse than not having a large memory   to begin with. So to avoid this, I'd have to calculate well   to make sure it does not run out of hash_area_size. Received on Thu Apr 17 2003 - 14:13:42 CDT

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