Documentation Source Text

  set aChng($nChng) [list $date $desc $options]
  set xrefChng($date) $nChng
  incr nChng
}

chng {2019-12-31 (3.31.0)} {
<li>Add support for [generated columns].
<li>Added the [sqlite3_hard_heap_limit64()] interface and the corresponding
    [PRAGMA hard_heap_limit] command.
<li>Faster response to [sqlite3_interrupt()].
<li>Added the [https://sqlite.org/src/file/ext/misc/uuid.c|uuid.c] extension module
    implementing functions for processing RFC-4122 UUIDs.
<li>The [legacy_file_format pragma] is deactivated.  It is now a no-op.  In its place,
    the [SQLITE_DBCONFIG_LEGACY_FILE_FORMAT] option to [sqlite3_db_config()] is
    provided.  The legacy_file_format pragma is deactivated because (1) it is
    rarely useful and (2) it is incompatible with [VACUUM] in schemas that have

    <p>^This pragma invokes the [sqlite3_soft_heap_limit64()] interface with
    the argument N, if N is specified and is a non-negative integer.
    ^The soft_heap_limit pragma always returns the same integer
    that would be returned by the [sqlite3_soft_heap_limit64](-1) C-language
    function.
    </p>
    <p>See also the [hard_heap_limit pragma].
}

Pragma hard_heap_limit {
    <p><b>PRAGMA hard_heap_limit<br>
          PRAGMA hard_heap_limit=</b><i>N</i></p>

    <p>^This pragma invokes the [sqlite3_hard_heap_limit64()] interface with
    the argument N, if N is specified and is positive integer that
    is less than the current hard heap limit.
    ^The hard_heap_limit pragma always returns the same integer
    that would be returned by the [sqlite3_hard_heap_limit64](-1) C-language
    function.  ^That is to say, it always returns the value of the hard
    heap limit that is set after any changes imposed by this PRAGMA.
    </p>

    <p>This pragma can only lower the heap limit, never raise it.
    The C-language interface [sqlite3_hard_heap_limit64()] must be used
    to raise the heap limit.</p>

    <p>See also the [soft_heap_limit pragma].
}

Pragma synchronous {
    <p>^(<b>PRAGMA DB.synchronous;
        <br>PRAGMA DB.synchronous = </b>
          <i>0 | OFF | 1 | NORMAL | 2 | FULL | 3 | EXTRA</i><b>;</b></p>

from becoming a denial-of-service attack, consider using the
[sqlite3_progress_handler()] interface to invoke a callback periodically
as each SQL statement runs, and have that callback return non-zero to
abort the statement if the statement runs for too long.  Alternatively,
set a timer in a separate thread and invoke [sqlite3_interrupt()] when
the timer goes off to prevent the SQL statement from running forever.

<li><p>
Limit the maximum amount of memory that SQLite will allocate using
the [sqlite3_hard_heap_limit64()] interface.  This helps prevent
denial-of-service attacks.  To find out how much heap space an
application actually needs, run the it against typical inputs and
then measure the maximum instantaneous memory usage with the 
[sqlite3_memory_highwater()] interface.  Set the hard heap limit
to the maximum observed instantaneous memory usage plus some margin.

<li><p>
In extreme cases, consider compiling SQLite with the
[-DSQLITE_ENABLE_MEMSYS5] option and then providing SQLite with
a fixed chunk of memory to use as its heap via the
[sqlite3_config]([SQLITE_CONFIG_HEAP]) interface. This will
prevent malicious SQL from executing a denial-of-service attack
by using an excessive amount of memory. If (say) 5 MB of memory
is provided for SQLite to use, once that much has been consumed,
SQLite will start returning SQLITE_NOMEM errors, rather than
soaking up memory needed by other parts of the application.
This also sandboxes SQLite's memory so that a write-after-free
error in some other part of the application will not cause
problems for SQLite, or vice versa.
</ol>

<h2>Untrusted SQLite Database Files</h2>

<p>Applications that accept untrusted database files should do the following:

<ol>
<li value="7"><p>
Run [PRAGMA integrity_check] or [PRAGMA quick_check] on the database
as the first SQL statement after opening the database files and
prior to running any other SQL statements.  Reject and refuse to
process any database file containing errors.

<li><p>
Enable the [PRAGMA cell_size_check=ON] setting.