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What does Imbed option do while defining a KSDS

 
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Madhu Kashyap

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Joined: 19 Jan 2006
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PostPosted: Thu Jan 19, 2006 2:30 pm    Post subject: What does Imbed option do while defining a KSDS
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Hi ,

Can anyone please tell me what does Imbed option do while defining a KSDS?
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senthils

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PostPosted: Thu Jan 19, 2006 2:48 pm    Post subject:
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Without replicate and Imbed, data CAs and CIs can be stored in different places on the disk from the index. This means that several I/Os are required for each access.

With Imbed and noreplicate, each data CA has its sequence set record at the front of the CA. If the CASZ is 1 cylinder then the sequence set is maintained on the 1st track of the cylinder. If the CASZ is less than 1 cylinder then one track is added to the CASZ. Thus, it costs 1 track per CA as the sequence set is written around the track as often as possible. Rotational delay is reduced as the r/w arm is placed above the sequence set and data. However, index updates cause an overhead as each copy of the sequence set has to be updated. Sequential processing benefits immensely from Imbed.

With replicate and noimbed, all data CAs and indexes are separate. Each higher level index is written as often as possible on a track. This option uses a lot of extra space and also requires extra I/O for index updates. If using this option the index should be allocated in cylinders and imbed should also be used. Since sequential processing only uses the sequence set, then replicate is of no value for sequential processing.
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Rupesh.Kothari

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PostPosted: Thu Jan 19, 2006 2:53 pm    Post subject: Re: Vsam Files
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HI,

Quote:
Can anyone please tell me what does Imbed option do while defining a KSDS?

I Read the following thing in one book regarding IMBED option.

This places the sequence set values in the first track, this will reduce the rotational time during access, so this is basically a performance issue.

Hope this helps

Regards
Rupesh
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Madhu Kashyap

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PostPosted: Thu Jan 19, 2006 3:15 pm    Post subject: Re: Vsam Files
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Thanks for answering my query.
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nagendrat

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PostPosted: Thu Jan 19, 2006 7:42 pm    Post subject: Re: What does Imbed option do while defining a KSDS
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The IMBED option places the index component's sequence set records in the space with the data component and causes the sequence set record to be duplicated as many times as possible on its track. This means that the first track of each control area will not be available for user data
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