#14058: Weakly reference binary operation codomains
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Reporter: robertwb | Owner: rlm
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.7
Component: memleak | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Robert Bradshaw | Merged in:
Dependencies: #12313 | Stopgaps:
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Comment (by SimonKing):
Replying to [comment:14 nbruin]:
> > I doubt that we want that. It is not desirable that, when adding
elements of `ZZ['x']` and QQ, the ring `QQ['x']` is created repeatedly
(OK, polynomial rings have a strong cache anyway. But you see what I
mean).
>
> In my opinion, that is exactly what we want, or at least what we have to
settle for. If a person wants to work efficiently with `QQ['x']` he should
ensure his elements already live there.
Granted. But it is a very typical usage to ''not'' explicitly convert
everything into a common parent, but let the coercion model do the work.
That is what the coercion model is for!
> I suspect that usually that will be the case, because if a user creates
elements somewhere regularly he probably
However, in the example that I posted above, note that multiplying
`OA(1)*OB(1)` repeatedly will also create `C()` ''repeatedly'', even
though it is a `UniqueRepresentation` and hence (weakly, nowadays) cached!
I think it is not acceptable that a multiple creation is triggered.
>
> In this scenario:
> {{{
> P=[ZZ['x%d'%i] for i in [1..1000]]
> F=[GF(p) for p in prime_range(1000)]
> for Zxi in P:
> for k in F:
> a=P.0
> b=F(1)
> c=a+b
> }}}
> If we keep the `GF(p)[xi]` alive because at some point we constructed an
element in it from parents that are still around, we've just created
quadratic memory requirements where linear should be enough.
In your example, `GF(p)[xi]` is created exactly once, for each value of p
and i. Clearly, in this situation it would not make sense to keep it
alive, because it is never reused. However, I doubt that this is a typical
use case.
> A limited length buffer that gets updated whenever a certain component
sees a parent go by might work. In Coercion ''discovery'' perhaps? That's
already slow and it would exactly protect these automatically generated
parents. Logically it's hard to defend but it may be OK in practice.
>
> Another possibility is just `UniqueRepresentation_c.__cinit__`. Only
when we're making a lot of parents do we care about losing them again ...
OK, but not all unique parent structures rely on it.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14058#comment:16>
Sage <http://www.sagemath.org>
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