[hibernate-dev] Redis and TTL

[Gunnar Morling]

Hi,

> [...] The TTL is not configured in OGM for this use-case because the TTL
might be determined somehow dynamic by the first client.

Yes, but this kind of issue is the crux when integrating different
applications through the database. If you can't avoid it, you at least
should use the same configurations within all the applications. Just as
e.g. column names, all applications syncing on one DB must be using the
same ones.

> So maybe we could address the TTL issue in a different way that is more
user-friendly and provide properties within an entity annotated with @TTL

That sounds interesting, could you describe in some more details how such
feature would be used? I could imagine some kind of "state-based" TTL
calculation, leaving it to the entity to return the TTL to use from some
annotated property. Is that what you had in mind?

Or maybe we could have some strategy of sort which determines
the behaviour for OGM writes:

    @Entity
    @TTL(value = 7, unit = TimeUnit.DAYS, strategy = REFRESH)
    public class Zoo { ... }

TtlStrategy.REFRESH would update the value to the given one for each write.
Another value such as KEEP would maintain the existing one to implement the
alternative behaviour. RERESH would be the default. On the downside, to
support no TTL being given via OGM at all and being able to work with KEEP,
we'd have to make value and unit optional. Maybe a separate annotation then?

--Gunnar


2016-06-27 16:39 GMT+02:00 Mark Paluch <mpaluch at paluch.biz>:

> Hi Sanne,
>
> not sure I follow.
>
> The use case is: Two applications (clients) share one Redis instance. The
> first (non-OGM) client writes some data and sets an expiry (TTL). The
> second (OGM) client updates the data stored inside of Redis and preserves
> the remaining TTL. Note that the first (non-OGM) client wrote an expiry and
> expects the key to disappear sooner or later.
>
> The TTL is not configured in OGM for this use-case because the TTL might
> be determined somehow dynamic by the first client.
>
> Greetings, Mark
>
> > Am 27.06.2016 um 15:52 schrieb Sanne Grinovero <sanne at hibernate.org>:
> >
> > Hi Mark,
> >
> > you wouldn't expect the timeout to be "reset" to some default value
> > when your code writes to an entity?
> >
> > If you could explain the use case, that might help us to understand this.
> >
> > Thanks,
> > Sanne
> >
> > On 27 June 2016 at 14:47, Mark Paluch <mpaluch at paluch.biz> wrote:
> >>
> >> Hi Guillaume,
> >>
> >> TTL preservation behavior originates from Redis’ behavior and is to
> preserve interoperability:
> >>
> >>> http://redis.io/commands/set <http://redis.io/commands/set>
> >>> Set key to hold the string value. [...] Any previous time to live
> associated with the key is discarded on successful SET operation.
> >>
> >>
> >> Keys written with SET loose their TTL value and the entry is persisted
> without any further TTL. Reading and re-applying TTL is to preserve the
> expiry.
> >> The general idea behind is to either apply the remaining TTL from the
> key, because TTL is not configured in the entity model or to set the
> configured TTL from the entity model.
> >> I see it from an integration-perspective in which Hibernate OGM and
> other tools share Redis data and so you’re opting-in for features but
> things are not broken.
> >>
> >> Best regards, Mark
> >>
> >>
> >>> Am 27.06.2016 um 14:43 schrieb Guillaume Smet <
> guillaume.smet at gmail.com>:
> >>>
> >>> Hi,
> >>>
> >>> So, I'm currently working on reducing the number of calls issued to
> Redis
> >>> in OGM as part of OGM-1064.
> >>>
> >>> At the moment, we execute a call to Redis to get the TTL already
> configured
> >>> on an object before saving it. If the TTL is not explicitly configured
> with
> >>> @TTL, we set this TTL again after having stored this entity (see
> >>> RedisJsonDialect#storeEntity). Same for associations stored in a
> different
> >>> document.
> >>>
> >>> In fact, this call returns the time remaining before expiration, not
> the
> >>> TTL previously configured,  so I find this behavior quite weird.
> Basically,
> >>> we store information which will expire sooner than expected. I can't
> really
> >>> get a use case for this and I don't think we should have an additional
> call
> >>> every time we store an object for a so obscure thing. Do we really
> expect
> >>> people to mess with TTLs of objects stored by OGM without relying on
> OGM
> >>> @TTL management?
> >>>
> >>> IMHO, we should get rid of this call and only deal with TTL when it's
> >>> configured via the @TTL annotation.
> >>>
> >>> Thoughts?
> >>>
> >>> --
> >>> Guillaume
> >>> _______________________________________________
> >>> hibernate-dev mailing list
> >>> hibernate-dev at lists.jboss.org
> >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev
> >>
> >> _______________________________________________
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> >> hibernate-dev at lists.jboss.org
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>
>
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