Page (File architecture): Difference between revisions

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A page is the underlying structure applied to the data-set(s) that comprise a Model 204 file.
A page is the underlying structure applied to the data sets that comprise a Model 204 file.


All pages are 6184 bytes.
All pages are 6184 bytes.
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* a 40 byte page trailer
* a 40 byte page trailer


 
== The page trailer ==
== The page Trailer ==


The page trailer contains:
The page trailer contains:


* the file name. This is the name used in the [[CREATE command: File|Create]] process  
* the file name, which is the name used in the [[CREATE command: File|create]] process  
* the date / time when the page was last [[INITIALIZE command|initialized]].
* the date / time when the page was last [[INITIALIZE command|initialized]]
* the date / time the page was last written to the file
* the date / time when the page was last written to the file
* data used in the [[CHECKPOINT command|checkpoint]] process
* data used in the [[CHECKPOINT command|checkpoint]] process
* the table that this page is part of (a numeric representation (see note 1))
* the table that this page is part of (a numeric representation as explained in Note 1 below)
* the sequential page number within the table
* the sequential page number within the table


Note 1: FCT = 00, Table A = 01, Table B = 02, Table C = 03, Table D = 04, Table E = 40 and Table X = 20.


Note 1: FCT = 00, Table A = 01, Table B = 02, Table C = 03, Table D = 04, Table E = 40 and Table X = 20. Because of INCREASE and DECREASE commands after the initial CREATE, the pages for a table may not be contiguous.   
Because of INCREASE and DECREASE commands after the initial CREATE, the pages for a table may not be contiguous.   




[[Category:File architecture]]
[[Category:File architecture]]

Revision as of 19:46, 16 May 2013

A page is the underlying structure applied to the data sets that comprise a Model 204 file.

All pages are 6184 bytes.

When a file is created, the pages in the file are formatted into:

  • 6144 bytes of 'usable' space (how the space is used depends on the table where the page resides)
  • a 40 byte page trailer

The page trailer

The page trailer contains:

  • the file name, which is the name used in the create process
  • the date / time when the page was last initialized
  • the date / time when the page was last written to the file
  • data used in the checkpoint process
  • the table that this page is part of (a numeric representation as explained in Note 1 below)
  • the sequential page number within the table

Note 1: FCT = 00, Table A = 01, Table B = 02, Table C = 03, Table D = 04, Table E = 40 and Table X = 20.

Because of INCREASE and DECREASE commands after the initial CREATE, the pages for a table may not be contiguous.