I have a feeling it may be time for me to learn some grown-up programming skills, and I hope someone here might be able to help.
I have a PHP script chewing over a large MySQL query. It's creating a handful of big associative arrays in the process, and punks out after the arrays get to 32MB.
Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 242 bytes) in analysis.php on line 41
I'm basically building a big associative array encoding the name of the borrowing institution, the patron type (student,faculty,staff,etc), the item barcode, and the various bits of data we want for each of these items.
// the first time we see a barcode
$stats[$inst][$patron_type][$item_barcode][first] = $date;
$stats[$inst][$patron_type][$item_barcode][min] = $renewals;
$stats[$inst][$patron_type][$item_barcode][call] = $call_no;
//subsequent instances of the barcode
$stats[$inst][$patron_type][$item_barcode][max] = $renewals;
Once I've chewed over all 4million records (40MB) , I spit it out into a new MySQL table that has the collated data that I want. Unfortunately this system breaks down when I get to so many millions of records.
Is there a more efficient way of doing this kind of data transformation? I *could* not keep so much in the big stats array and instead make millions of "UPDATE" calls to the MySQL table, but that doesn't sound like a winning proposition to me. I imagine that I could also increase the memory allotment, but it will eventually get to big too. Or I suppose that I could do it all in chunks - right now I'm parsing the whole raw-data SQL table at once; I could do one institution's data at a time and buy myself some wiggle-room.
But fundamentally, it seems to me that asking PHP to hold lots of data in an array might not be the most programmerly system; it's just what I've always done.