does database chunk() have a memory leak?

Question

In laravel, I have a query that searches thousands of rows in a database, and I trying to compile that into a CSV file. In attempt to reduce memory usage, I get 500 rows at a time and output the CSV.

 $callback = function () use ($query) {
 $file = fopen('php://output', 'w');
 $query->chunk(500, function ($rows) use ($file) {
 foreach ($rows as $key => $row) {
 fputcsv($file, array_map(...$rows...));
 }
 log_info("Memory used " . memory_get_usage());
 });
 fclose($file);
 };
 $headers = [ ... ];
 return response()->stream($callback, 200, $headers);

The actual query is a bit more complex, and involves getting related models which also need to be rehydrated. When I run this, it begins generating the CSV file and, after a while, runs out of memory. This is in my log

(59): Memory used 17208328;
(59): Memory used 25105328;
(59): Memory used 30601328;
...
(59): Memory used 127380496;
(59): Memory used 129352584;
(59): Memory used 131207672;
[2025年11月23日 23:50:15] qa.ERROR: Allowed memory size of 134217728 bytes exhausted (tried to allocate 16384 bytes) 

What I Tried

I tried putting the following inside the chunk loop, hoping that it would free memory. It had no effect on the memory consumption.

 unset($rows);
 flush();
 gc_collect_cycles();

• apokryfos: Since you are writing to the output it's possible you have buffered output on. Try running ob_end_clean() before you start streaming the response to see if that makes a difference
• mankowitz: I added ob_end_clean() but no luck. I would think that flush() would release that memory
• MultiSuperFreek: How much rows are in the CSV? Since you are writing to php://output, this writes to the output buffer (keyword being buffer), so if the output exceeds 128MB, it will trip the memory limit (but 128MB is a lot of text).