Description:
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I don't have any kind of simple repro for this, unfortunately. I'm trying to upgrade an app from 5.6 to 7.0. The app works fine in 7.0 for some period of time and then every single mysqli connection attempt starts failing with this error:

Warning: mysqli::mysqli(): (HY000/2002): An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full.

As far as I can tell this is the result of the OS itself running out of memory for TCP buffers (https://blogs.msdn.microsoft.com/sql_protocols/2009/03/09/understanding-the-error-an-operation-on-a-socket-could-not-be-performed-because-the-system-lacked-sufficient-buffer-space-or-because-a-queue-was-full/). I'm not using either of the ini switches mention in the Microsoft article. This problem does not occur using 5.6 with the same app on the same system.

I'm seeing this issue with exactly one client browser executing PHP scripts via HTTP requests. Closing the client browser and waiting for several minutes does not seem to release any resources. Once the error occurs it continues to occur on every connection attempt until Apache is restarted.

I'm using the 32bit, thread-safe 7.0.7 build from windows.php.net with 32-bit apache 2.4.20 binaries from Apache Lounge.

Besides mysqli, I'm enabling php_opcache as well as these extensions: curl, gettext, intl, mbstring, openssl, sockets, xsl.