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<title>Impose A Limit On Heap Size</title>
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<!-- keywords: sqlite3_hard_heap_limit64 sqlite3_soft_heap_limit64 -->
<div class=nosearch>
<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
<h2>Impose A Limit On Heap Size</h2>
</div>
<blockquote><pre>
sqlite3_int64 sqlite3_soft_heap_limit64(sqlite3_int64 N);
sqlite3_int64 sqlite3_hard_heap_limit64(sqlite3_int64 N);
</pre></blockquote>
<p>
These interfaces impose limits on the amount of heap memory that will be
by all database connections within a single process.</p>
<p>The sqlite3_soft_heap_limit64() interface sets and/or queries the
soft limit on the amount of heap memory that may be allocated by SQLite.
SQLite strives to keep heap memory utilization below the soft heap
limit by reducing the number of pages held in the page cache
as heap memory usages approaches the limit.
The soft heap limit is "soft" because even though SQLite strives to stay
below the limit, it will exceed the limit rather than generate
an <a href="../rescode.html#nomem">SQLITE_NOMEM</a> error. In other words, the soft heap limit
is advisory only.</p>
<p>The sqlite3_hard_heap_limit64(N) interface sets a hard upper bound of
N bytes on the amount of memory that will be allocated. The
sqlite3_hard_heap_limit64(N) interface is similar to
sqlite3_soft_heap_limit64(N) except that memory allocations will fail
when the hard heap limit is reached.</p>
<p>The return value from both sqlite3_soft_heap_limit64() and
sqlite3_hard_heap_limit64() is the size of
the heap limit prior to the call, or negative in the case of an
error. If the argument N is negative
then no change is made to the heap limit. Hence, the current
size of heap limits can be determined by invoking
sqlite3_soft_heap_limit64(-1) or sqlite3_hard_heap_limit(-1).</p>
<p>Setting the heap limits to zero disables the heap limiter mechanism.</p>
<p>The soft heap limit may not be greater than the hard heap limit.
If the hard heap limit is enabled and if sqlite3_soft_heap_limit(N)
is invoked with a value of N that is greater than the hard heap limit,
the soft heap limit is set to the value of the hard heap limit.
The soft heap limit is automatically enabled whenever the hard heap
limit is enabled. When sqlite3_hard_heap_limit64(N) is invoked and
the soft heap limit is outside the range of 1..N, then the soft heap
limit is set to N. Invoking sqlite3_soft_heap_limit64(0) when the
hard heap limit is enabled makes the soft heap limit equal to the
hard heap limit.</p>
<p>The memory allocation limits can also be adjusted using
<a href="../pragma.html#pragma_soft_heap_limit">PRAGMA soft_heap_limit</a> and <a href="../pragma.html#pragma_hard_heap_limit">PRAGMA hard_heap_limit</a>.</p>
<p>The heap limits are not enforced in the current implementation
if one or more of following conditions are true:</p>
<p><ul>
<li> The limit value is set to zero.
<li> Memory accounting is disabled using a combination of the
<a href="../c3ref/config.html">sqlite3_config</a>(<a href="../c3ref/c_config_covering_index_scan.html#sqliteconfigmemstatus">SQLITE_CONFIG_MEMSTATUS</a>,...) start-time option and
the <a href="../compile.html#default_memstatus">SQLITE_DEFAULT_MEMSTATUS</a> compile-time option.
<li> An alternative page cache implementation is specified using
<a href="../c3ref/config.html">sqlite3_config</a>(<a href="../c3ref/c_config_covering_index_scan.html#sqliteconfigpcache2">SQLITE_CONFIG_PCACHE2</a>,...).
<li> The page cache allocates from its own memory pool supplied
by <a href="../c3ref/config.html">sqlite3_config</a>(<a href="../c3ref/c_config_covering_index_scan.html#sqliteconfigpagecache">SQLITE_CONFIG_PAGECACHE</a>,...) rather than
from the heap.
</ul></p>
<p>The circumstances under which SQLite will enforce the heap limits may
changes in future releases of SQLite.
</p><p>See also lists of
<a href="../c3ref/objlist.html">Objects</a>,
<a href="../c3ref/constlist.html">Constants</a>, and
<a href="../c3ref/funclist.html">Functions</a>.</p>
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