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Question on ISN -- Adabas

 
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nartcr

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Joined: 06 Jun 2007
Posts: 78
Location: anada

PostPosted: Thu Nov 22, 2012 9:05 pm    Post subject: Question on ISN -- Adabas
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Hello,

I am learning Natural and Adabas through manuals.. There is something i do not understand from the manuals,and i am trying to find the answer in Vain. Its regd how a data is stored in Adabas.

I took the below table from Adabas documentation. If you notice the ISN 10, ISN 11 and ISN 12, it resides on same block number, but it contains different data. I was under the impression that ISN would be unique for the data record until it is reassigned or when data gets deleted. Would you be able to examine the below table -- blk size 237, and let me know how same ISN would be used by ADABAS for storing different datarecord. And possibly what would address convertor contain in such case?

Code:

Blk ISN  PER-ID  FIRST-NM  LST-NAME  DEPT  BIRTH 

234   1   11400316   WILLI    BEUSE    MARK29    390509
234   2   11400314   ERHARD    BECKER    SALE47    540707
234   13  11300307   JAN    KAMAL    SALE37    590328
235   4   11400312   INGRID    SCHMID    MARK19    540308
235   5   11400310   MARGAR   GROTH    MARK29    540623
235   6   11400307   JOSEFA    LEYRER COMP28    410407
236   7   11400304   MARIAN    RACKMAN COMP28    541209
236   9   11300319   SULEYM    YALCIN    SALE37    580819
237   10  11300316   GABRIEL KANTE    SALE47    540809
237   11  11300315   GUDRUN    FRIESE    SALE37    560504
237   12  11300314   GITTA    MOHRD SALE17    390912
298   8   11400303   MARTIN    WALLIN  COMP28    460921
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Garry Carroll

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Joined: 08 May 2006
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Location: Dublin, Ireland / Edinburgh, Scotland

PostPosted: Thu Nov 22, 2012 9:11 pm    Post subject:
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The ISN in all cases shown is unique. It's the BLK that is the same and, in this case, it looks like a block can accommodate three records and BLK 234 has had record 3 replaced by record 13. Record 8 is, for some reason, in an out-of-sequence block.

Garry.
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nartcr

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Location: anada

PostPosted: Thu Nov 22, 2012 9:16 pm    Post subject:
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Thanks Gary, I realised that when i copied the table into my word, it rearranged itself making ISN out of sequence ( BLK Size came on ISN column and ISN went into BLKSIZE column ). Thanks a lot.
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Ralph Zbrog

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Location: California

PostPosted: Fri Nov 23, 2012 12:06 pm    Post subject: Reply to: Question on ISN -- Adabas
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ISN is a unique identifier for a record within a file. A record's ISN does not change. But let's say that I add Ralph to my customer file, and Adabas assigns ISN 7. Someone deletes customer Ralph, but I wish to reinstate him. When I add Ralph a second time, there is no reason for me to believe that ISN 7 will be assigned again. As far as Adabas is concerned, two unique records have been created.

During initial load of a file, ISNs will be assigned sequentially. Otherwise ISN assignment is dependent upon Adabas file settings. Unless the data records are quite large, multiple records will fit into each block. During initial load of a file, records are loaded into sequential blocks. Otherwise block assignment is dependent upon Adabas file settings. For various reasons, over time a record may migrate from one block to another.

In the example given, ISN 8 migrated from block 236 to 298. ISN 3 either migrated or was deleted, and its space in block 234 was re-used by ISN 13.
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