Custom controller very slow for some users, really slow for others

Question

We have built a custom controller for a customer which passed products data and loads their products in a custom url.

The controllers are basically like this:

class CustomProducts(http.Controller):
    @http.route('/custom', type='http', auth='public', website=True, methods=['GET'])
    def render_custom_products(self, **kw):

        if kw.get('order'):
          if kw.get('order') != "":
            order_by = kw.get('order')
        else:
          order_by = 'list_price desc'

        products = http.request.env['product.product'].sudo().search([('categ_id.name', 'ilike', 'Custom'), ('is_published', '=', 'true'), ('active', '=', 'true')],
        order= order_by,
        limit = 150)
        return http.request.render('custom_module.custom_products', {
          # pass products details to view
          'products': products,
          })

EDIT: This has worked good for over 2 years but suddenly the page is very slow. The weird thing is that the route is very slow for some visitors and very fast (like before) for some. What could be the issue?

Postgres sometimes gives this error: Could not serialize access due to concurrent update SELECT * FROM website_visitor where id = XX FOR NO KEY UPDATE NOAWAIT

The customer only have between 30-50 products for sale at once.

Answer 1

I really cant make good sense of the solution but it was changing the images in the Qweb view to not display the images using base encoding but to load the images by their URL.

Old:

t-att-src="'data:image/png;base64,%s' % to_text(product.image_512)"

Working:

t-attf-src="/web/image/product.product/{{product.id}}/image_512"

I still dont understand why it was quick for some users and for some sessions on the same machines.