Page (File architecture): Difference between revisions
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When a file is [[Creating a file (File management)|created]], the pages in the file are formatted into: | When a file is [[Creating a file (File management)|created]], the pages in the file are formatted into: | ||
<ul> | |||
<li>6144 bytes of "usable" space (how the space is used depends on the table where the page resides) | |||
<li>A 40 byte page trailer | |||
</ul> | |||
==The page trailer== | |||
The page trailer contains the following: | |||
<ul> | |||
<li>The file name, which is the name used in the [[CREATE command: File|create]] process. </li> | |||
<li>The date/time when the page was last [[INITIALIZE command|initialized]]. </li> | |||
The page | <li>The date/time when the page was last written to the file. </li> | ||
<li>Data used in the [[CHECKPOINT command|checkpoint]] process. </li> | |||
<li>The table that this page is part of, the numeric representation for which is as follows: | |||
Because of INCREASE and DECREASE commands after the initial CREATE, the pages for a table might not be contiguous. | <p>FCT = 00, Table A = 01, Table B = 02, Table C = 03, Table D = 04, Table E = 40, and Table X = 20. </p> </li> | ||
<li>The sequential page number within the table. | |||
<p> | |||
Because of <var>[[INCREASE command|INCREASE]]</var> and <var>[[DECREASE command|DECREASE]]</var> commands after the initial <var>CREATE</var>, the pages for a table might not be contiguous. </p> </li> | |||
</ul> | |||
[[Category:File architecture]] | [[Category:File architecture]] | ||
Revision as of 17:26, 24 January 2014
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 following:
- 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, the numeric representation for which is as follows:
FCT = 00, Table A = 01, Table B = 02, Table C = 03, Table D = 04, Table E = 40, and Table X = 20.
- The sequential page number within the table.
Because of INCREASE and DECREASE commands after the initial CREATE, the pages for a table might not be contiguous.