MongoDB PHP Driver 1.15+ increases PHP memory consumption

[jazzsequence]

Bug Report

We (Pantheon / https://github.com/pantheon-systems) compile PHP manually and build a variety of extensions into our PHP image. Recently, I attempted updating MongoDB from 1.14.2 (what we were previously using) to 1.16.2 and received reports that PHP was taking much longer to resolve according to New Relic data. Rolling back to 1.15.x did not resolve, but the difference can be seen after we reverted back to 1.14.2:

We don't actually run MongoDB but provide the driver for users who wish to make MongoDB connections.

Environment

OS: Centos 8 / Debian 20.10.7 PHP: 8+ https://v80-php-info.pantheonsite.io/ https://v81-php-info.pantheonsite.io/ https://v82-php-info.pantheonsite.io/ (We're currently in the process of rolling back the MongoDB driver update on the platform, so the above phpinfo sites may or may not show 1.16/1.14)

Happy to provide any other details I can. I will say that after the update, I needed to manually install libbson and libmongoc, so my suspicion is that those updates are related.