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wht are the advantages of VSAM files compared to flat files

 
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santhunaveen

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Joined: 22 Sep 2006
Posts: 33

PostPosted: Tue Mar 13, 2007 3:54 pm    Post subject: wht are the advantages of VSAM files compared to flat files
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Hi,

Can any one tell me how can we identify..is this a VSAM file or a flat file.....

And wht are the advantages of VSAM files compared to flat files.....?
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Aryang4u

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Joined: 21 Feb 2006
Posts: 8
Location: Los Angels, CA

PostPosted: Tue Mar 13, 2007 5:26 pm    Post subject:
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We wont be able to open a VSAM file in ISPF option 3.4.
So when we try the same you will get a error message like

"VSAM processing unavail. ".
We can view the same using Fileaid

Hope this helps you to easily differentiate both.

------------------------------------------------------------------------

Advantages:-

1. Data Retrieval is fast in VSAM.
2. Record management is easy compared with Sequential dataset.
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dick scherrer

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Joined: 23 Nov 2006
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PostPosted: Tue Mar 13, 2007 8:09 pm    Post subject:
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Hello,

Vsam files are defined as a cluster and flat files are not. For one vsam file, there are multiple physical files (the "master" file, the data file, and a file for index entries).

The biggest advantages with vsam are the ability to read records randomly based on a key (there may be multiple keys) and the ability to access the vsam file in batch and online concurrently.
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Aryang4u

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PostPosted: Tue Mar 13, 2007 11:23 pm    Post subject: Re: wht are the advantages of VSAM files compared to flat fi
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Thanks a lot Dick for better clarification.
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dick scherrer

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PostPosted: Tue Mar 13, 2007 11:30 pm    Post subject:
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You're welcome icon_smile.gif
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Anuj Dhawan

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Joined: 22 Apr 2006
Posts: 6258
Location: Mumbai, India

PostPosted: Sat Mar 17, 2007 11:50 pm    Post subject:
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Hi,

Let say you have a VSAM file HLQ.VSAM.FILE, If you use ISPF then if you try to open this file with 3.4 option then, you will get 3 files as:

HLQ.VSAM.FILE **VSAM**
HLQ.VSAM.FILE.DATA VOLUME NO.
HLQ.VSAM.FILE.INDEX VOLUME NO.

Here if you put 'B', to browse, in front of VSAM file 'DITTO' funtion will invoke. If will open using F1 option user will be asked about proper layout.

For a flat file, browse will simply browse the file.

These are the differences, can help you to differentiate between VSAM & Flat file from ISPF point of view.

Further VSAM is of 3 types: ESDS, KSDS,RRDS.


As stated by Dick, uses of keys make random access of data in VSAMs, which is not possible in Flat File.
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