PHP is getting a native doubly-linked list structure. This is fabulous news; when I wrote the File_MARC PEAR package, I ended up having to implement a linked list class in PEAR to support it. File_MARC does its job today (even though I haven't taken it out of alpha yet), but due to its reliance on userspace data structures it's an order of magnitude slower than packages like marc4j so it's not the best choice for processing hundreds of thousands of MARC records... today. It hurts a little that the VuFind project has to use a non-PHP solution for populating its Solr indices - although I'm delighted that they have started using File_MARC for some on-demand processing.
Now, when I get a chance (insert raucous mocking laughter here), I hope to be able to make File_MARC use splDoublyLinkedList and see how it fares with 500K records. Should be good fun! After that, it just needs to be taught how to convert MARC8 to UTF-8, and we'll have ourselves a fully featured standard MARC package for PHP.