Documentation Source Text

  <h2>Glossary</h2>
    <p class=todo>
      After this document is ready, make the vocabulary consistent and
      then add a glossary here.

<h1 id=vfs_assumptions>VFS Adaptor Related Assumptions</h1>

  <p>
    This section documents those assumptions made about the system that
    the VFS adaptor provides access to. The assumptions noted in section
    <cite>fs_characteristics</cite> are particularly important. If these
    assumptions are not true, then a power or operating system failure
    may cause SQLite databases to become corrupted.

  <h2>Performance Related Assumptions</h2>

    <p>
      SQLite uses the assumptions in this section to try to speed up 
      reading from and writing to the database file.

    ASSUMPTION A21010
      It is assumed that writing a series of sequential blocks of data to 
      a file in order is faster than writing the same blocks in an arbitrary
      order.

  <h2 id=fs_characteristics>System Failure Related Assumptions</h2>
    <p>

            <li> the remaining operations will not have had any effect on
                 the contents of the file-system.
          </ol> 
    </ul>

    <h3>Failure Related Assumption Details</h3>





    <p>
      This section describes how the assumptions presented in the parent
      section apply to the individual API functions and operations provided 
      by the VFS to SQLite for the purposes of modifying the contents of the
      file-system.

    <p>

      then it is assumed that the content of all sectors spanned by the
      <i>write file</i> operation are untrustworthy following system 
      recovery. This includes regions of the sectors that were not
      actually modified by the write file operation.

    ASSUMPTION A21011
      If a system failure occurs on a system that supports the 
      <i>atomic-write</i> property for blocks of size <i>N</i> bytes
      following an aligned write of <i>N</i> 
      bytes to a file but before the file has been succesfully <i>synced</i>,
      then is is assumed following recovery that all sectors spanned by the
      write operation were correctly updated, or that none of the sectors were
      modified at all.

    ASSUMPTION A21012
      If a system failure occurs on a system that supports the 

    ASSUMPTION A21009
      If a system failure occurs during or after a "write file"
      operation that causes the file to grow, but before the corresponding 
      file has been <i>synced</i>, then it is assumed that the size of 
      the file following recovery is as large or larger than it was before 
      the "write file" operation that, if successful, would cause the file 
      to grow.

    <p>
      If a system supports the <i>sequential-write</i> property, then further
      assumptions may be made with respect to the state of the file-system
      following recovery from a <i>system failure</i>. Specifically, it is
      assumed that create, truncate, delete and write file operations are
      applied to the persistent representation in the same order as they 
      are performed by SQLite. Furthermore, it is assumed that the 
      file-system waits until one operation is safely written to the 
      persistent media before the next is attempted, just as if the relevant
      file were <i>synced</i> following each operation.

    ASSUMPTION A21014
      If a system failure occurs on a system that supports the
      <i>sequential-write</i> property, then it is assumed that all 
      operations completed before the last time any file was <i>synced</i> 
      have been successfully committed to persistent media.

    ASSUMPTION A21015
      If a system failure occurs on a system that supports the
      <i>sequential-write</i> property, then it is assumed that the set
      of possible states that the file-system may be in following recovery
      is the same as if each of the write operations performed since the most
      recent time a file was <i>synced</i> was itself followed by a <i>sync
      file</i> operation, and that the system failure may have occured during
      any of the write or <i>sync file</i> operations.


<!--
    <p>
      The return value of the xSectorSize() method, the <i>sector-size</i>, is
      expected by SQLite to be a power of 2 value greater than or equal to 512.

    <p class=todo>