Page (File architecture): Difference between revisions
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A page is the underlying structure applied to the data | 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 | |||
The page trailer contains: | The page trailer contains: | ||
* the file name | * 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 | * 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. | |||
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.