I have a PHP script that builds a binary search tree over a rather large CSV file (5MB+). This is nice and all, but it takes about 3 seconds to read/parse/index the file.
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It seems that the answer to your question is no.
Even if you discover a "binary serialization format" option most likely even that would be to slow for what you envisage.
So, what you may have to look into using (as others have mentioned) is a database, memcached, or on online web service.
I'd like to add the following ideas as well: