Documentation Source Text

      written to the file system just before or during the failure. The exact
      combination of IO operations that SQLite is required to perform in 
      order to safely modify a database file depend on the exact 
      characteristics of the target platform.

    <p>
      This section describes the assumptions that SQLite makes about the
      the content of a file-system following a power or system failure. In
      other words, it describes the extent of file and file-system corruption
      that such an event may cause.

    <p>
      SQLite queries an implementation for file-system characteristics
      using the xDeviceCharacteristics() and xSectorSize() methods of the
      database file file-handle. These two methods are only ever called
................................................................................

    ASSUMPTION A21004
      If a system failure occurs during a "delete file" operation,
      it is assumed that following system recovery the file-system will 
      either contain the file being deleted in the state it was in before
      the operation was attempted, or not contain the file at all. It is 
      assumed that it is not possible for the file to have become corrupted
      purely as a result of a failure occurfing during a "delete file" 
      operation.

    <p>
      The effects of a <b>truncate file</b> operation are not assumed to
      be made persistent until after the corresponding file has been
      <i>synced</i>.

      written to the file system just before or during the failure. The exact
      combination of IO operations that SQLite is required to perform in 
      order to safely modify a database file depend on the exact 
      characteristics of the target platform.

    <p>
      This section describes the assumptions that SQLite makes about the
      content of a file-system following a power or system failure. In
      other words, it describes the extent of file and file-system corruption
      that such an event may cause.

    <p>
      SQLite queries an implementation for file-system characteristics
      using the xDeviceCharacteristics() and xSectorSize() methods of the
      database file file-handle. These two methods are only ever called
................................................................................

    ASSUMPTION A21004
      If a system failure occurs during a "delete file" operation,
      it is assumed that following system recovery the file-system will 
      either contain the file being deleted in the state it was in before
      the operation was attempted, or not contain the file at all. It is 
      assumed that it is not possible for the file to have become corrupted
      purely as a result of a failure occurring during a "delete file" 
      operation.

    <p>
      The effects of a <b>truncate file</b> operation are not assumed to
      be made persistent until after the corresponding file has been
      <i>synced</i>.

        the value that can be interpreted as an integer number is extracted from
        the TEXT value and the remainder ignored. ^Any leading spaces in the
        TEXT value when converting from TEXT to INTEGER are ignored. ^If there
        is no prefix that can be interpreted as an integer number, the result
        of the conversion is 0.

      <p>^A cast of a REAL value into an INTEGER will truncate the fractional
      part of the REAL.  ^If an REAL is too large to be represented as an 
      INTEGER then the result of the cast is the largest negative integer: 
      -9223372036854775808.

<tr>
  <td> NUMERIC
  <td> ^Casting a TEXT or BLOB value into NUMERIC first does a forced
   conversion into REAL but then further converts the result into INTEGER if

        the value that can be interpreted as an integer number is extracted from
        the TEXT value and the remainder ignored. ^Any leading spaces in the
        TEXT value when converting from TEXT to INTEGER are ignored. ^If there
        is no prefix that can be interpreted as an integer number, the result
        of the conversion is 0.

      <p>^A cast of a REAL value into an INTEGER will truncate the fractional
      part of the REAL.  ^If a REAL is too large to be represented as an 
      INTEGER then the result of the cast is the largest negative integer: 
      -9223372036854775808.

<tr>
  <td> NUMERIC
  <td> ^Casting a TEXT or BLOB value into NUMERIC first does a forced
   conversion into REAL but then further converts the result into INTEGER if

be handled in all circumstances.
</p>

<p>
So instead of going by the standards documents, various popular
SQL engines were tested to see how they handle NULLs.  The idea
was to make SQLite work like all the other engines.
A SQL test script was developed and run by volunteers on various
SQL RDBMSes and the results of those tests were used to deduce
how each engine processed NULL values.
The original tests were run in May of 2002.
A copy of the test script is found at the end of this document.
</p>

<p>

be handled in all circumstances.
</p>

<p>
So instead of going by the standards documents, various popular
SQL engines were tested to see how they handle NULLs.  The idea
was to make SQLite work like all the other engines.
An SQL test script was developed and run by volunteers on various
SQL RDBMSes and the results of those tests were used to deduce
how each engine processed NULL values.
The original tests were run in May of 2002.
A copy of the test script is found at the end of this document.
</p>

<p>

<em>&lt;name&gt;</em><strong>_node</strong><br>
<em>&lt;name&gt;</em><strong>_rowid</strong><br>
<em>&lt;name&gt;</em><strong>_parent</strong>
</blockquote>)^

<p>
^The shadow tables are ordinary SQLite data tables.  You can query them 
directly if you like, though this unlikely to to reveal anything particularly
useful. 
^And you can [UPDATE], [DELETE], [INSERT] or even [DROP TABLE | DROP] 
the shadow tables, though doing so will corrupt your R*Tree index.
So it is best to simply ignore the shadow tables.  Recognize that they
are there to hold your R*Tree index information and let it go as that.
</p>

<em>&lt;name&gt;</em><strong>_node</strong><br>
<em>&lt;name&gt;</em><strong>_rowid</strong><br>
<em>&lt;name&gt;</em><strong>_parent</strong>
</blockquote>)^

<p>
^The shadow tables are ordinary SQLite data tables.  You can query them 
directly if you like, though this unlikely to reveal anything particularly
useful. 
^And you can [UPDATE], [DELETE], [INSERT] or even [DROP TABLE | DROP] 
the shadow tables, though doing so will corrupt your R*Tree index.
So it is best to simply ignore the shadow tables.  Recognize that they
are there to hold your R*Tree index information and let it go as that.
</p>