PDO auto-instrumentation reports span.subtype = unknown_DB for Pdo\Pgsql (and other PDO subclasses) on PHP 8.4

[abelharisov]

Environment

PHP 8.4.19
apm-agent-php 1.15.1
Laravel 13.14.0
PostgreSQL via ext-pdo_pgsql

Describe the bug
After upgrading to PHP 8.4, DB spans in Kibana APM show span.subtype = unknown_DB instead of postgresql. Service Map no longer shows PostgreSQL as a dependency. Redis spans are unaffected.

To Reproduce

1. PHP 8.4 + ext-pdo_pgsql + apm-agent-php 1.15.1
2. Run:

$pdo = PDO::connect('pgsql:host=localhost;dbname=test', 'user', 'pass');
$pdo->query('SELECT 1');

3. Open the resulting DB span in Kibana APM.

Expected behavior
span.subtype = "postgresql", connection visible as PostgreSQL dependency in Service Map.

Actual behavior
span.subtype = "unknown_DB".

Possible cause
PHP 8.4 introduced driver-specific PDO subclasses (RFC) — new PDO('pgsql:...') now returns a Pdo\Pgsql instance instead of plain PDO. The agent hooks PDO methods by the hardcoded class name 'PDO', so the constructor interceptor does not fire on the subclass, the DSN is never parsed, and dbType falls back to unknown_DB. Likely affects all PHP 8.4 PDO subclasses (Pdo\Mysql, Pdo\Sqlite, etc.).

[m13v]

this is the class-name-vs-class-hierarchy hook problem, and it'll bite every PHP APM agent through 2026 as 8.4 adoption climbs. the RFC also lets userland register custom Pdo subclasses, so 'just add Pdo\Pgsql, Pdo\Mysql, Pdo\Sqlite' is a band-aid that misses the long tail. durable fix is hooking by inheritance (is_subclass_of, or any class with PDO in the ancestor chain) and parsing the DSN off the connected instance, not assuming the constructor fired on literal PDO. same pattern hits Doctrine/DBAL bound to mysqli or pgsql class names.