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Can we tell DFSORT the input dataset is already sorted?

 
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feng hao

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Joined: 26 Mar 2008
Posts: 44
Location: China

PostPosted: Tue Dec 22, 2009 12:36 pm    Post subject: Can we tell DFSORT the input dataset is already sorted?
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I used ICETOOL's select operator and I found it would sort in advance by the the 'ON(key)' before it do the subsequent real select operaton.

Then, my question is, could we tell DFSORT when we invoke it that the input dataset is already sorted correctly and it could do the real selection work directly?

Though I don't know the detail operation undergoing, I think it must save time and space when dealing with huge datasets.

Best regards!
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Frank Yaeger

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Joined: 15 Feb 2005
Posts: 7130
Location: San Jose, CA

PostPosted: Tue Dec 22, 2009 9:15 pm    Post subject:
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If the input records are already in sorted order by the ON fields, you can tell DFSORT to do a copy instead of a sort by using OPTION COPY. For example:

Code:

...
//TOOLIN DD *
SELECT ... USING(CTL1)
//CTL1CNTL DD *
   OPTION COPY


A copy operation is generally more efficient than a sort operation.
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feng hao

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Joined: 26 Mar 2008
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PostPosted: Wed Dec 23, 2009 11:53 am    Post subject:
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Hi, Frank,

It works after adding 'option copy'. I found that 16 sortwk* are not allocated again and elapsed time has decreased from 2.64s to 0.82s!!!
There is no difference in the storage size both below and above the line, however, that is not the topic here.

Thanks very much, Frank!
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Frank Yaeger

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Joined: 15 Feb 2005
Posts: 7130
Location: San Jose, CA

PostPosted: Wed Dec 23, 2009 9:01 pm    Post subject:
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Yes, work data sets are NOT dynamically allocated or used for a COPY application.
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