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karthick Ramesh
New User
Joined: 19 Mar 2008
Posts: 12
Location: India
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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: 792
Location: Chennai, India
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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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Joined: 19 Mar 2008
Posts: 12
Location: India
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| Thank you Gnanas!!! |
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expat
Global Moderator
Joined: 14 Mar 2007
Posts: 8797
Location: Welsh Wales
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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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Joined: 06 Sep 2007
Posts: 792
Location: Chennai, India
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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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