I have to perform a query that can generates a very big string in response (up to 1Gb), which is basically a big, big JSON array. Yes, pagination is in order but I'm stressing the concept in order to get you the idea. Symfony simply uses doctrine to get the response:
$stmt = $this->getEntityManager()->getConnection()->prepare(self::Q_GET_NUM_TIMEBOX);
$stmt->bindValue('t_end', $tEnd);
$stmt->bindValue('t_granularity', $tGranularity);
$stmt->bindValue('t_span', $varSelection->getStart());
$stmt->execute();
$resData = $stmt->fetchColumn(0);
and then I create a Response by setting the content I had in return from the execute.
$res = new Response();
$res->setStatusCode(200);
$res->headers->set('Content-Type', 'application/json');
$res->setContent($resData);
Keep in mind I oversimplified the code for the sake of clarity: I actually have a controller, a handler service performing the request and a Repository returning the query response.
Back straight to the problem: this implies that PHP must hold that big amount of data in memory and I was wondering if there was an lighter way to return the response in order to stress less PHP engine with big amount of data.
this implies that PHP must hold that big amount of data
PHP is not required to keep in the memory a whole response body. Through output buffers and Symfony response streaming you can fetch result set row-by-row and send a data by chunks. Unfortunately I don't known well-tried solution for JSON stream encoding in PHP, but you can implement it manually (1, 2).
Update (2017-02-27):
Streaming JSON Encoder is a PHP library that provides a set of classes to help with encoding JSON in a streaming manner, i.e. allowing you to encode the JSON document bit by bit rather than encoding the whole document at once.