WordPress 4.9.8 Beta two recently shipped and although much of the focus will be on the “Try Gutenberg” call-out, there’s a patch included that addresses a memory leak that was quite a problem for some users.
The bug is actually in PHP and is related to the stream-get-wrappers function. WordPress 4.9.7 increased the number of times it calls the wp_is_stream() function generating the error more often.
Bailing if the path isn’t a stream. This isn’t perfect: it’s still possible to trigger the PHP bug, but it does significantly reduce the chances of the bug being encountered. For many WordPress sites (those that don’t have plugins that use streams), it reduces the chance to zero.
If you encountered memory exhaustion errors after installing or upgrading to WordPress 4.9.7, try WordPress 4.9.8 Beta 2 to see if it fixes the issue.
Aside from coming up with a solution, Trac ticket #44532 is a bit refreshing to see. In open source, tickets or issues can get bogged down with suggestions, hypothetical scenarios, and bike-shed commentary.
In this instance, the issue was identified and folks from the community along with core contributors worked together in a focused fashion to create a fix in time for the next point release. The ticket is a good example of what it’s like when open source is firing on all cylinders.