Why is my Ruby On Rails database query so slow? - ruby-on-rails

Question

The following code always uses more then ten seconds. I have upgraded the server, but it doesn't help. I know I have some database design problems, but I can't modify that.
I am showing all the prices from differents locations of products of a category also in different time range, because the prices change every 15 days in each location.
controller
def prods_x_cat
# This will load all the products of a category
#products = Product.prods_x_cat(params[:id],:include => :raw_datas)
#cortes = RawData.cortes
respond_to do |format|
format.js { render :layout=>false}
end
end
prods_x_cat.js.erb
var jqxhr1 = $.ajax($("#loading_overlay .loading_message, #loading_overlay").fadeIn());
$('#datos').html("<%= escape_javascript render :partial=>'/shared/prods_x_cat'%>")
view
<%#cortes.each do |c|%>
<%=c.corte%>
<%end%>
<%#cortes.each do |c|%>
<%#fecha = c.corte_real%>
<div id="<%=c.corte%>" class="block no_padding">
<table class="display datatable">
<thead>
<tr>
<th>SKU</th>
<%Company.active.order('table_field ASC').each do |c|%>
<th><%=c.abbr%></th>
<%end%>
<th>Average</th>
<th>Mode</th>
<th>Minimum</th>
<th>Maximum</th>
</tr>
</thead>
<tbody>
<%#products.each do |p|%>
<tr class="gradeA">
<td><%=p.name%></td>
<%p.raw_datas.where("product_id='#{p.id}' and corte_real='#{#fecha}'").each do |prd|%>
<td><%=prd.location1.to_f.round(2)%></td>
<td><%=prd.location2.to_f.round(2)%></td>
<td><%=prd.location3.to_f.round(2)%></td>
<td><%=prd.location4.to_f.round(2)%></td>
<td><%=prd.location5.to_f.round(2)%></td>
<td><%=prd.location6.to_f.round(2)%></td>
<td><%=prd.location7.to_f.round(2)%></td>
<td><%=prd.location8.to_f.round(2)%></td>
<td><%=prd.promedio.to_f.round(2)%></td>
<td><%=prd.moda%></td>
<td><%=prd.minimo.to_f.round(2)%></td>
<td><%=prd.maximo.to_f.round(2)%></td>
<%end%>
</tr>
<%end%>
</tbody>
</table>
</div>
<%end%>
</div>

Answer 1

This kind of question is pretty much impossible to answer without seeing all the code involved. Instead I can help you try to figure out where the problem is.
There are good tools for finding where your performance problems are (e.g. ruby-prof) but if you want a quick primitive way to find where your issue is, just use Time.now. For example, you could change your controller action to be:
def prods_x_cat
# This will load all the products of a category
a1 = Time.now
#products = Product.prods_x_cat(params[:id],:include => :raw_datas)
b1 = Time.now
p "Time for finding products: #{b1 - a1}"
a2 = Time.now
#cortes = RawData.cortes
b2 = Time.now
p "Time for finding cortes: #{b2 - a2}"
respond_to do |format|
format.js { render :layout=>false}
end
end
If the printouts suggest that the time is taken up elsewhere, start doing something similar in your template. Focus on the database calls.