Repository navigation
OCI_RETURN_LOBS flag causes oci8 to leak memory #18873
Description
Description
The following code:
$expectedStr = str_repeat('a', 1_001);
$sql = 'select concat(TO_CLOB(\'' . str_repeat('a', 1_000) . '\'), TO_CLOB(\'a\')) AS "v" from "DUAL"';
$memUsages = array_flip(range(0, 100 - 1));
foreach (array_keys($memUsages) as $k) {
$stid = oci_parse($c, $sql);
oci_execute($stid);
$row = oci_fetch_array($stid, \OCI_ASSOC | \OCI_RETURN_LOBS);
$res = $row['v'];
if ($res !== $expectedStr) {
var_dump([$expectedStr, $res]);
throw new \Exception('unexpected result');
}
$memUsages[$k] = memory_get_usage();
}
$memUsages = array_slice($memUsages, 1, null, true);
$memUsages = array_unique($memUsages);
if (count($memUsages) !== 1) {
var_dump($memUsages);
throw new \Exception('memory leak detected');
}
echo "ok\n";
https://raw.githubusercontent.com/php/pecl-database-oci8/9a1241341cd02aa68c587046f11b0343bc713b8f/tests/gh-4-return-lob.phpt (2 lines changed of https://raw.githubusercontent.com/php/pecl-database-oci8/9a1241341cd02aa68c587046f11b0343bc713b8f/tests/gh-4.phpt already present test)
Resulted in this output:
array(9) {
[1]=>
int(6872016)
[2]=>
int(6872368)
[3]=>
int(6872400)
[4]=>
int(6872432)
[5]=>
int(6872464)
...
}
PHP Fatal error: Uncaught Exception: memory leak detected in ...
But I expected this output instead:
ok
Notes:
php/pecl-database-oci8#29 fixed memory leak once after 8th descriptor create, and such fix can be backported into PHP 8.3 however it is not critical and maybe it can be even considered a feature.
This issue is about a clear memory leak after every iteration when the data are fetched using OCI_RETURN_LOBS flag. Such flag imply the data are not returned as descriptor, but as a string instead. So it seems the descriptor is somehow not released after the data are read.
PHP Version
PHP 8.2 - master
Operating System
any (tested linux and Windows)
Activity
mvorisek commentedon Jun 19, 2025
The only usafe of the problematic
OCI_RETURN_LOBSflag is in https://github.com/php/php-src/blob/php-8.3.22/ext/oci8/oci8.c#L1571. Any idea what is wrong with this part of code?SakiTakamachi commentedon Jun 27, 2025
This is a matter of when the
descriptor, which is azend_resource, gets freed.First, regardless of the
OCI_RETURN_LOBSflag, thedescriptor's reference count is decremented inphp_oci_column_hash_dtor(). If the reference count is1at that point,zend_list_close()is called.However, since it is called when the reference count is
1, this alone does not fully destroy the resource. As a result, remnants remain until the end of the script, leading to increased memory usage.php-src/ext/oci8/oci8.c
Line 577 in e892356
When the
OCI_RETURN_LOBSflag is not used, memory usage remains stable because thedescriptoris registered as a property of azend_object(which increases the reference count by1). In this case,zend_list_close()is not called inphp_oci_column_hash_dtor(), it simply decrements the reference count.Subsequently, the
descriptoris destroyed along with the destruction of thezend_object, so it does not persist until the end of the script.php-src/ext/oci8/oci8.c
Line 1596 in e892356
Fix GH-18873 - Free column->descid appropriately (#18957)
Merge branch 'PHP-8.3' into PHP-8.4
Merge branch 'PHP-8.4'