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Re: When does a merge join beat a hash join?

From: Telemachus <telemachus_at_ulysseswillreturn.net>
Date: Wed, 5 Mar 2003 10:53:54 -0000
Message-ID: <7Hk9a.441$pK2.788@news.indigo.ie>

  1. Because a: the optimizer thought MJ was cheaper or b: ruled HJ out.

2 : A fairly sweeping statment - don't know the size of the inputs or what they look like therefore can't answer the question

3: Probably Mr. Lewis is the man to answer this one... "Jaap W. van Dijk" <j.w.vandijk.removethis_at_hetnet.nl> wrote in message news:tjeb6vk2brd93jtbuopirauuset9g2vimq_at_4ax.com...
> A general (theoretical? academical?) question:
>
> When the Oracle optimizer chooses a merge join, why doesn't it choose
> a hash join instead?
> Shouldn't a hash join always be faster than a merge join?
> And if it isn't, is that because of poorly chosen parameter values, or
> are there data situations in which it is inherent that a merge join is
> faster than a hash join?
>
> Jaap.
Received on Wed Mar 05 2003 - 04:53:54 CST

Original text of this message

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