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sqlite的帮助文档

<p><b>SQLITE_THREADSAFE=<i>&lt;0 or 1 or 2&gt;</i></b></p><blockquote><p>
  This option controls whether or not code is included in SQLite to
  enable it to operate safely in a multithreaded environment.  The
  default is SQLITE_THREADSAFE=1 which is safe for use in a multithreaded
  environment.  When compiled with SQLITE_THREADSAFE=0 all mutexing code
  is omitted and it is unsafe to use SQLite in a multithreaded program.
  When compiled with SQLITE_THREADSAFE=2, SQLite can be used in a multithreaded
  program so long as no two threads attempt to use the same
  <a href="c3ref/sqlite3.html">database connection</a> at the same time.</p>

<p>  To put it another way, SQLITE_THREADSAFE=1 sets the default
  <a href="threadsafe.html">threading mode</a> to Serialized.  SQLITE_THREADSAFE=2 sets the default
  <a href="threadsafe.html">threading mode</a> to Multi-threaded.  And SQLITE_THREADSAFE=0 sets the
  <a href="threadsafe.html">threading mode</a> to Single-threaded.</p>

<p>  The value of SQLITE_THREADSAFE can be determined at run-time
  using the <a href="c3ref/threadsafe.html">sqlite3_threadsafe()</a> interface.</p>

<p>  When SQLite has been compiled with SQLITE_THREADSAFE=1 or
  SQLITE_THREADSAFE=2 then the <a href="threadsafe.html">threading mode</a>
  can be altered at run-time using the <a href="c3ref/config.html">sqlite3_config()</a> interface together
  with one of these verbs:</p>

<p>  <ul>
  <li><a href="c3ref/c_config_getmalloc.html">SQLITE_CONFIG_SINGLETHREAD</a>
  <li><a href="c3ref/c_config_getmalloc.html">SQLITE_CONFIG_MULTITHREAD</a>
  <li><a href="c3ref/c_config_getmalloc.html">SQLITE_CONFIG_SERIALIZED</a>
  </ul></p>

<p>  The <a href="c3ref/c_open_create.html">SQLITE_OPEN_NOMUTEX</a> and
  <a href="c3ref/c_open_create.html">SQLITE_OPEN_FULLMUTEX</a> flags to <a href="c3ref/open.html">sqlite3_open_v2()</a> can also be used
  to adjust the <a href="threadsafe.html">threading mode</a> of individual <a href="c3ref/sqlite3.html">database connections</a>
  at run-time.</p>

<p>  Note that when SQLite is compiled with SQLITE_THREADSAFE=0, the code
  to make SQLite threadsafe is omitted from the build.  When this occurs,
  it is impossible to change the <a href="threadsafe.html">threading mode</a> at start-time or run-time.</p>

<p>  See the <a href="threadsafe.html">threading mode</a> documentation for additional information
  on aspects of using SQLite in a multithreaded environment.
</p></blockquote><a name="temp_store"></a>
<p><b>SQLITE_TEMP_STORE=<i>&lt;0 through 3&gt;</i></b></p><blockquote><p>
  This option controls whether temporary files are stored on disk or
  in memory.  The meanings for various settings of this compile-time
  option are as follows:</p>

<p>  <table cellpadding="2" border="1">
  <tr><th>SQLITE_TEMP_STORE</th><th>Meaning</th></tr>
  <tr><td align="center">0</td><td>Always use temporary files</td></tr>
  <tr><td align="center">1</td><td>Use files by default but allow the
  <a href="pragma.html#pragma_temp_store">PRAGMA temp_store</a> command to override</td></tr>
  <tr><td align="center">2</td><td>Use memory by default but allow the
  <a href="pragma.html#pragma_temp_store">PRAGMA temp_store</a> command to override</td></tr>
  <tr><td align="center">3</td><td>Always use memory</td></tr>
  </table></p>

<p>  The default setting is 1.  
  Additional information can be found in <a href="tempfiles.html#tempstore">tempfiles.html</a>.
</p></blockquote>

<a name="enablefeatures"></a>
<h2>1.4 Options To Enable Features Normally Turned Off</h2>

<a name="enable_atomic_write"></a>
<p><b>SQLITE_ENABLE_ATOMIC_WRITE</b></p><blockquote><p>
  If this C-preprocessor macro is defined and if the
  xDeviceCharacteristics method of <a href="c3ref/io_methods.html">sqlite3_io_methods</a> object for
  a database file reports (via one of the <a href="c3ref/c_iocap_atomic.html">SQLITE_IOCAP_ATOMIC</a> bits)
  that the filesystem supports atomic writes and if a transaction
  involves a change to only a single page of the database file,
  then the transaction commits with just a single write request of
  a single page of the database and no rollback journal is created
  or written.  On filesystems that support atomic writes, this
  optimization can result in significant speed improvements for
  small updates.  However, few filesystems support this capability
  and the code paths that check for this capability slow down write
  performance on systems that lack atomic write capability, so this
  feature is disabled by default.
</p></blockquote><a name="enable_column_metadata"></a>
<p><b>SQLITE_ENABLE_COLUMN_METADATA</b></p><blockquote><p>
  When this C-preprocessor macro is defined, SQLite includes some
  additional APIs that provide convenient access to meta-data about
  tables and queries.  The APIs that are enabled by this option are:</p>

<p>  <ul>
  <li> <a href="c3ref/column_database_name.html">sqlite3_column_database_name()</a> </li>
  <li> <a href="c3ref/column_database_name.html">sqlite3_column_database_name16()</a> </li>
  <li> <a href="c3ref/column_database_name.html">sqlite3_column_table_name()</a> </li>
  <li> <a href="c3ref/column_database_name.html">sqlite3_column_table_name16()</a> </li>
  <li> <a href="c3ref/column_database_name.html">sqlite3_column_origin_name()</a> </li>
  <li> <a href="c3ref/column_database_name.html">sqlite3_column_origin_name16()</a> </li>
  <li> <a href="c3ref/table_column_metadata.html">sqlite3_table_column_metadata()</a> </li>
  </ul>
</p></blockquote><a name="enable_fts3"></a>
<p><b>SQLITE_ENABLE_FTS3</b></p><blockquote><p>
  When this option is defined in the <a href="amalgamation.html">amalgamation</a>, version 3
  of the full-text search engine is added to the build automatically.
</p></blockquote><a name="enable_icu"></a>
<p><b>SQLITE_ENABLE_ICU</b></p><blockquote><p>
  This option causes the 
  <a href="http://www.icu-project.org/">International Components for Unicode</a>
  or "ICU" extension to SQLite to be added to the build.  
</p></blockquote><a name="enable_iotrace"></a>
<p><b>SQLITE_ENABLE_IOTRACE</b></p><blockquote><p>
  When both the SQLite core and the <a href="sqlite.html">Command Line Interface</a> (CLI) are both 
  compiled with this option, then the CLI provides an extra command
  named ".iotrace" that provides a low-level log of I/O activity.
  This option is experimental and may be discontinued in a future release.
</p></blockquote><a name="enable_locking_style"></a>
<p><b>SQLITE_ENABLE_LOCKING_STYLE</b></p><blockquote><p>
  This option enables additional logic in the OS interface layer for
  Mac OS X. The additional logic attempts to determine the type of the
  underlying filesystem and choose and alternative locking strategy
  that works correctly for that filesystem type. Five locking strategies 
  are available:</p>

<p>  <ul>
    <li> POSIX locking style. This is the default locking style and the
         style used by other (non Mac OS X) Unixes. Locks are obtained and 
         released using the fcntl() system call.</p>

<p>    <li> AFP locking style. This locking style is used for network file 
         systems that use the AFP (Apple Filing Protocol) protocol. Locks
         are obtained by calling the library function _AFPFSSetLock().</p>

<p>    <li> Flock locking style. This is used for file-systems that do not
         support POSIX locking style. Locks are obtained and released using
         the flock() system call.</p>

<p>    <li> Dot-file locking style. This locking style is used when neither
         flock nor POSIX locking styles are supported by the file system.
         Database locks are obtained by creating and entry in the file-system
         at a well-known location relative to the database file (a "dot-file")
         and relinquished by deleting the same file.</p>

<p>    <li> No locking style. If none of the above can be supported, this 
         locking style is used. No database locking mechanism is used. When
         this system is used it is not safe for a single database to be
         accessed by multiple clients.
  </ul></p>

<p>  Additionally, five extra VFS implementations are provided as well as the
  default. By specifying one of the extra VFS implementations 
  when calling <a href="c3ref/open.html">sqlite3_open_v2()</a>, an application may bypass the file-system
  detection logic and explicitly select one of the above locking styles. The
  five extra VFS implementations are called "unix-posix", "unix-afp",
  "unix-flock", "unix-dotfile" and "unix-none".
</p></blockquote><a name="enable_memory_management"></a>
<p><b>SQLITE_ENABLE_MEMORY_MANAGEMENT</b></p><blockquote><p>
  This option adds extra logic to SQLite that allows it to release unused
  memory upon request.  This option must be enabled in order for the
  <a href="c3ref/release_memory.html">sqlite3_release_memory()</a> interface to work.  If this compile-time
  option is not used, the <a href="c3ref/release_memory.html">sqlite3_release_memory()</a> interface is a 
  no-op.  Since <a href="c3ref/soft_heap_limit.html">sqlite3_soft_heap_limit()</a> depends on
  <a href="c3ref/release_memory.html">sqlite3_release_memory()</a>, this option is also necessary for
  the correct operation of <a href="c3ref/soft_heap_limit.html">sqlite3_soft_heap_limit()</a>.
</p></blockquote><a name="enable_memsys3"></a>
<p><b>SQLITE_ENABLE_MEMSYS3</b></p><blockquote><p>
  This option includes code in SQLite that implements an alternative
  memory allocator.  This alternative memory allocator is only engaged
  when the <a href="c3ref/c_config_getmalloc.html">SQLITE_CONFIG_HEAP</a> option to <a href="c3ref/config.html">sqlite3_config()</a> is used to
  supply a large chunk of memory from which all memory allocations are
  taken.
  The MEMSYS3 memory allocator uses a hybrid allocation algorithm 
  patterned after dlmalloc().   Only one of SQLITE_ENABLE_MEMSYS3 and 
  SQLITE_ENABLE_MEMSYS5 may be enabled at once.
</p></blockquote><a name="enable_memsys5"></a>
<p><b>SQLITE_ENABLE_MEMSYS5</b></p><blockquote><p>
  This option includes code in SQLite that implements an alternative
  memory allocator.  This alternative memory allocator is only engaged
  when the <a href="c3ref/c_config_getmalloc.html">SQLITE_CONFIG_HEAP</a> option to <a href="c3ref/config.html">sqlite3_config()</a> is used to
  supply a large chunk of memory from which all memory allocations are
  taken.
  The MEMSYS5 module rounds all allocations up to the next power
  of two and uses a first-fit, buddy-allocator algorithm
  that provides strong guarantees against fragmentation and breakdown
  subject to certain operating constraints.
</p></blockquote><a name="enable_rtree"></a>
<p><b>SQLITE_ENABLE_RTREE</b></p><blockquote><p>
  This option causes SQLite to include support for the
  <a href="rtree.html">R*Tree index extension</a>.
</p></blockquote><a name="enable_update_delete_limit"></a>
<p><b>SQLITE_ENABLE_UPDATE_DELETE_LIMIT</b></p><blockquote><p>
  This option enables an optional ORDER BY and LIMIT clause on 
  <a href="lang_update.html">UPDATE</a> and <a href="lang_delete.html">DELETE</a> statements.</p>

<p>  <p>If this option is defined, then it must also be 
  defined when using the 'lemon' tool to generate a parse.c
  file. Because of this, this option may only be used when the library is built
  from source, not from the <a href="amalgamation.html">amalgamation</a> or from the collection of
  pre-packaged C files provided for non-Unix like platforms on the website.
  </p>
</p></blockquote><a name="yytrackmaxstackdepth"></a>
<p><b>YYTRACKMAXSTACKDEPTH</b></p><blockquote><p>
  This option causes the LALR(1) parser stack depth to be tracked
  and reported using the <a href="c3ref/status.html">sqlite3_status</a>(<a href="c3ref/c_status_malloc_size.html">SQLITE_STATUS_PARSER_STACK</a>,...)
  interface.  SQLite's LALR(1) parser has a fixed stack depth
  (determined at compile-time using the <a href="compile.html#yystackdepth">YYSTACKDEPTH</a> options).
  This option can be used to help determine if an application is
  getting close to exceeding the maximum LALR(1) stack depth.
</p></blockquote>

<a name="disablefeatures"></a>
<h2>1.5 Options To Disable Features Normally Turned On</h2>

<a name="disable_lfs"></a>
<p><b>SQLITE_DISABLE_LFS</b></p><blockquote><p>
  If this C-preprocessor macro is defined, large file support