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What is OSAM file?

 
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karthick Ramesh

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Joined: 19 Mar 2008
Posts: 12
Location: India

PostPosted: Fri Mar 28, 2008 12:04 pm    Post subject: What is OSAM file?
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Hi can any one Explain what is OSAM file. Im just want to know about it out of my curiosity i have came across this, but it not a part of any of my requirements.
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Gnanas N

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Joined: 06 Sep 2007
Posts: 788
Location: Chennai, India

PostPosted: Fri Mar 28, 2008 12:15 pm    Post subject:
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Karthick,

OSAM stands for Overflow Sequential Access Method.

Converting VSAM databases to OSAM increases the addressing capability twice that of VSAM and requires no change in current application program and PSB with minor change in DBD.

It can support addressing or indexing capacity up tp 8 GB per partition where as VSAM is limited to 4GB.

So, OSAM is one of the large datebase alternatives.

At right now I am working on this for IMS databases.
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karthick Ramesh

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PostPosted: Fri Mar 28, 2008 12:26 pm    Post subject:
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Thank you Gnanas!!!
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expat

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PostPosted: Fri Mar 28, 2008 12:40 pm    Post subject:
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Quote:
where as VSAM is limited to 4GB.

Using SMS Extended ability the 4GB limit on VSAM was removed with (I think) z/OS 1.2 or 1.3
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Gnanas N

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PostPosted: Fri Mar 28, 2008 4:39 pm    Post subject:
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Yes, Expat.

With the release of DFSMS/MVS 1.3, if VSAM data set is SMS-managed and defined as extended format(to use EA), the new size limit for an EA data set is determined by either
1. multiplying the CI size by 4 GB
2. multiplying the volume size by 59


The original limit was based on a 4-byte Relative Byte Address (RBA), but the new system uses an 8-byte RBA that creates a new limit of 128TB.
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