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Overview
Comment:Further changes to fileformat.html.
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: 6631cb911ef50d5d8ecffafc3833016b96195d92
User & Date: dan 2009-04-07 18:27:15
Context
2009-04-07
18:34
Merge two leaves. check-in: 17aaeb85f9 user: dan tags: trunk
18:27
Further changes to fileformat.html. check-in: 6631cb911e user: dan tags: trunk
15:34
Incremental updates to fileformat.html. check-in: 8b1e897acb user: dan tags: trunk
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Changes to pages/fileformat.in.

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               sequence of bytes is:
                 <pre>0xd9 0xd5 0x05 0xf9 0x20 0xa1 0x63 0xd7</pre>
    </table>

[h3 "Master-Journal File Details" masterjournal_file_format]

[h2 "Reading an SQLite Database" reading_from_files]


















































[h2 "Writing to an SQLite Database" writing_to_files]

  <p>
    When an SQLite user commits a transaction that modifies the contents
    of the database, the database representation on disk must be modified
    to reflect the new contents of the database. SQLite is required to do







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               sequence of bytes is:
                 <pre>0xd9 0xd5 0x05 0xf9 0x20 0xa1 0x63 0xd7</pre>
    </table>

[h3 "Master-Journal File Details" masterjournal_file_format]

[h2 "Reading an SQLite Database" reading_from_files]

  <p>
    As described in section <cite>pages_and_page_types</cite> of this document,
    an SQLite database image is a set of contiguously numbered fixed size 
    pages. The numbering starts at 1, not 0. Page 1 contains the 
    <i>database file header</i> and the root page of the <i>schema table</i>, 
    and all other pages within the database image are somehow referred to 
    by number from page 1, either directly or indirectly.
    
  <p>
    Usually, the <i>database file</i> contains the complete, unadulterated 
    <i>database image</i>. When this is the case, the file offset of each 
    database page can be calculated based on its page number. Reading the
    contents of a <i>database page</i> is a simple matter of reading a
    block of <i>page-size</i> bytes from the calculated offset. However, if 
    there is a <i>journal file</i> corresponding to the <i>database file</i>
    present within the file-system then the situation can be more 
    complicated. The current data for each page of the <i>database image</i>
    may currently be stored within the <i>database file</i> at a file offset
    based on its page number as it normally is, or the current version of
    the data may be stored somewhere within the <i>journal file</i>.

  <ol>
    <li> <p>If the <i>journal file</i> contains a well-formed 
      <i>master-journal pointer</i>, and the <i>master-journal</i> is either
      not present in the file-system or it does not contain the name of
      the <i>journal file</i>, then the contents of the <i>journal file</i>
      are invalid. The <i>database file</i> contains the database image
      verbatim.

    <li> <p>If the first 28 bytes of the <i>journal file</i> do not contain
      a well-formed <i>journal header</i>, or they contain a well-formed
      <i>journal header</i> with the <i>record count</i> field set to zero,
      then the contents of the <i>journal file</i> are invalid. As in case
      1 above, the <i>database file</i> contains the database image verbatim.




      <li> <p>If the first 28 bytes of the <i>journal file</i> contain a
      well-formed <i>journal header</i> with a non-zero value for the <i>record
      count</i> field, then the <i>page-size</i> used by the <i>database
      image</i> is as stored at byte offset 24 of the <i>journal header</i>.
      The size of the database image in pages is as stored at byte offset 16 of
      the <i>journal header</i>.


  </ol>


[h2 "Writing to an SQLite Database" writing_to_files]

  <p>
    When an SQLite user commits a transaction that modifies the contents
    of the database, the database representation on disk must be modified
    to reflect the new contents of the database. SQLite is required to do