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From Michael Gentry <mgen...@masslight.net>
Subject Re: Best Practice Question
Date Fri, 30 Mar 2012 12:33:22 GMT
Hi Joe,

I think you are on the right path using setPageSize() to limit the
result set, but even 50k results is a lot of PKs to return (although
not a ludicrous amount, depending on your users).

The first approach I would take is if they do a post-query sort then
send another query to the database with the new sort ordering in place
and let the database do it.

Let's say you have 50,000 results and a page size of 20.  50,000 / 20
= 2500 pages.  For you to to sort in-memory using that paginated list
would require 2499 trips to the database to fetch the records and make
Java objects out of them (I'm assuming you showed them the first page
already and they sorted then, so the first page is "free").  2499
queries will be a killer latency-wise, even if each query is quick.  I
think it'll be significantly faster to let the database do it,
especially if you have good indexes in place.

mrg


On Thu, Mar 29, 2012 at 8:29 PM, Joe Baldwin <jfbaldwin@earthlink.net> wrote:
> I am interested in the best practice wrt ordering in a certain context.
>
> Lets say the context is a store with 1000 - 50000 items. I understand that if I can either
include the "order by" directive pre-query or post query.  Also, I understand that if I have
a opportunity, then passing the "order by" to the DBMS is Cayenne-preferred (because, as I
understand it) Cayenne can retrieve the result set ordered, and minimize the triggering of
faults resulting in minimum memory usage.  I think I understand this scenario, and have tried
to code to this strategy.
>
> The second scenario is a tad more complex and really the subject of my concern.  Note,
if the result set is small, I believe that this is of no concern.  However, web-users do
not often care about setting off "totally insane queries".  So if a query is initiated with
'give me everything you have', then once they see the result set (which I am trying to manage
with setPageSize()), they might *then* want to sort the result set (i.e. triggering a "orderList()"
which is an in-memory ordering which is not as efficient).
>
> So given the post-query sorting requirement, a large result set, using setPageSize(),
and possibly multiple different post-sorts being initiated, what is the best-practice?  Should
I resubmit these queries with the ordering, or simply use the orderList() method on the result
set?  Or, is there another strategy for optimizing coding for these requirements?
>
> (My intuition, base on reading about Cayenne is that I just need to rely on orderList()
and buy more server memory. - but I am not sure)
>
> Thanks Joe
>

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