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Posted to dev@tomcat.apache.org by Rainer Jung <ra...@kippdata.de> on 2011/07/10 21:38:47 UTC
Distributable contexts and non-serializable session attributes
I implemented an addition to DeltaManager which allows to filter which
session attributes actually get replicated (not yet committed).
This is useful, because many applications
- use non-serializable session attributes, so
it is not possible to simply replicate everything
- do not actually need everything replicated, because they
can bootstrap all they need from a login context if a filter
detects, that a failover has happened.
In these cases it can also help to reduce replication traffic a lot.
Unfortunately I stu,bled into some code in StandardSession:
public void setAttribute(String name, Object value, boolean notify) {
...
if ((manager != null) && manager.getDistributable() &&
!(value instanceof Serializable))
throw new IllegalArgumentException
(sm.getString("standardSession.setAttribute.iae", name));
...
}
This means if you enable "distributable", then you can no longer set any
non-serializable session attribute. The code is not recent, it goes back
to at least TC 3.3.
I understand, that it is helpful to devs being informed about
serialization/replication problems. But I think it is too strict to
enforce this in StandardSession whch is the base class of all our
cluster sessions and we always delegate to
StandardSession.setAttribute() after some cluster specific handling.
The SPEC says:
The container must accept objects that implement the Serializable interface.
- The container may choose to support storage of other designated
objects in the
HttpSession, such as references to Enterprise JavaBeans components and
transactions.
- Migration of sessions will be handled by container-specific facilities.
The distributed servlet container must throw an IllegalArgumentException for
objects where the container cannot support the mechanism necessary for
migration
of the session storing them.
(and some more in 7.7.2).
I think checking for serializability in StandardSession isn't good,
because AFAIK StandardSession isn't used by any mechanism Tomcat
supports to implement "distributable".
And in DeltaSession I would like to have the check optional, i.e. only
check if the configuration wants the attribute to be replicated.
By default all attributes will be replicated as is today, but by
configuration one will be able to choose attributes to replicate using a
regexp against the attribute name.
Any remarks?
Rainer
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Re: Distributable contexts and non-serializable session attributes
Posted by Christopher Schultz <ch...@christopherschultz.net>.
Rainer,
On 7/10/2011 3:38 PM, Rainer Jung wrote:
> Unfortunately I stumbled into some code in StandardSession:
>
> public void setAttribute(String name, Object value, boolean notify) {
> ...
> if ((manager != null) && manager.getDistributable() &&
> !(value instanceof Serializable))
> throw new IllegalArgumentException
> (sm.getString("standardSession.setAttribute.iae", name));
> ...
> }
>
> This means if you enable "distributable", then you can no longer set any
> non-serializable session attribute. The code is not recent, it goes back
> to at least TC 3.3.
>
> I think checking for serializability in StandardSession isn't good,
> because AFAIK StandardSession isn't used by any mechanism Tomcat
> supports to implement "distributable".
>
> And in DeltaSession I would like to have the check optional, i.e. only
> check if the configuration wants the attribute to be replicated.
>
> By default all attributes will be replicated as is today, but by
> configuration one will be able to choose attributes to replicate using a
> regexp against the attribute name.
+1
-chris
Re: Distributable contexts and non-serializable session attributes
Posted by Rainer Jung <ra...@kippdata.de>.
On 11.07.2011 13:41, Konstantin Kolinko wrote:
> 2011/7/10 Rainer Jung <ra...@kippdata.de>:
>>
>> I think checking for serializability in StandardSession isn't good,
>> because AFAIK StandardSession isn't used by any mechanism Tomcat
>> supports to implement "distributable".
>>
>> And in DeltaSession I would like to have the check optional, i.e. only
>> check if the configuration wants the attribute to be replicated.
>>
>> By default all attributes will be replicated as is today, but by
>> configuration one will be able to choose attributes to replicate using a
>> regexp against the attribute name.
>>
>> Any remarks?
>>
>
> I think you are right and we can relax the requirement.
> E.g. to delegate the check to some helper method that is overwritten
> in DeltaSession or in other derived class.
Thanks, will do!
Regards,
Rainer
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Re: Distributable contexts and non-serializable session attributes
Posted by Konstantin Kolinko <kn...@gmail.com>.
2011/7/10 Rainer Jung <ra...@kippdata.de>:
> I implemented an addition to DeltaManager which allows to filter which
> session attributes actually get replicated (not yet committed).
>
> This is useful, because many applications
>
> - use non-serializable session attributes, so
> it is not possible to simply replicate everything
>
> - do not actually need everything replicated, because they
> can bootstrap all they need from a login context if a filter
> detects, that a failover has happened.
>
> In these cases it can also help to reduce replication traffic a lot.
>
> Unfortunately I stu,bled into some code in StandardSession:
>
> public void setAttribute(String name, Object value, boolean notify) {
> ...
> if ((manager != null) && manager.getDistributable() &&
> !(value instanceof Serializable))
> throw new IllegalArgumentException
> (sm.getString("standardSession.setAttribute.iae", name));
> ...
> }
>
> This means if you enable "distributable", then you can no longer set any
> non-serializable session attribute. The code is not recent, it goes back
> to at least TC 3.3.
>
> I understand, that it is helpful to devs being informed about
> serialization/replication problems. But I think it is too strict to
> enforce this in StandardSession whch is the base class of all our
> cluster sessions and we always delegate to
> StandardSession.setAttribute() after some cluster specific handling.
>
> The SPEC says:
>
> The container must accept objects that implement the Serializable interface.
> - The container may choose to support storage of other designated
> objects in the
> HttpSession, such as references to Enterprise JavaBeans components and
> transactions.
> - Migration of sessions will be handled by container-specific facilities.
> The distributed servlet container must throw an IllegalArgumentException for
> objects where the container cannot support the mechanism necessary for
> migration
> of the session storing them.
>
> (and some more in 7.7.2).
>
> I think checking for serializability in StandardSession isn't good,
> because AFAIK StandardSession isn't used by any mechanism Tomcat
> supports to implement "distributable".
>
> And in DeltaSession I would like to have the check optional, i.e. only
> check if the configuration wants the attribute to be replicated.
>
> By default all attributes will be replicated as is today, but by
> configuration one will be able to choose attributes to replicate using a
> regexp against the attribute name.
>
> Any remarks?
>
I think you are right and we can relax the requirement.
E.g. to delegate the check to some helper method that is overwritten
in DeltaSession or in other derived class.
Best regards,
Konstantin Kolinko
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Re: Distributable contexts and non-serializable session attributes
Posted by Mark Thomas <ma...@apache.org>.
On 11/07/2011 14:50, Rainer Jung wrote:
> On 10.07.2011 23:11, Filip Hanik - Dev Lists wrote:
>> go ahead add it in, if you add in a flag to toggle the behavior, and the
>> flag is defaulted to today's behavior. you're safe, and you give users
>> an option
>
> Thanks for the feedback. I will go with Konstantin's suggestion of
> making it overwritable by any extension of StandardSession via putting
> the check in a protected method.
>
> The default impl will be unchanged, but DeltaSession can do something else.
>
> Again by default DeltaSession will just call super, but when the
> attribute replication filtering is on, it will only check if the
> attribute matches the filter.
>
> And now on to hacking ...
>
> Mark: no need to wait for that w.r.t. 7.0.19.
ack.
I'm still working my way through the issues I do need to fix for 7.0.19.
Next stop, the TCK failure.
Mark
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Re: Distributable contexts and non-serializable session attributes
Posted by Rainer Jung <ra...@kippdata.de>.
On 10.07.2011 23:11, Filip Hanik - Dev Lists wrote:
> go ahead add it in, if you add in a flag to toggle the behavior, and the
> flag is defaulted to today's behavior. you're safe, and you give users
> an option
Thanks for the feedback. I will go with Konstantin's suggestion of
making it overwritable by any extension of StandardSession via putting
the check in a protected method.
The default impl will be unchanged, but DeltaSession can do something else.
Again by default DeltaSession will just call super, but when the
attribute replication filtering is on, it will only check if the
attribute matches the filter.
And now on to hacking ...
Mark: no need to wait for that w.r.t. 7.0.19.
Regards,
Rainer
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Re: Distributable contexts and non-serializable session attributes
Posted by Filip Hanik - Dev Lists <de...@hanik.com>.
go ahead add it in, if you add in a flag to toggle the behavior, and the flag is defaulted to today's behavior. you're safe, and you give
users an option
Filip
On 7/10/2011 1:38 PM, Rainer Jung wrote:
> I implemented an addition to DeltaManager which allows to filter which
> session attributes actually get replicated (not yet committed).
>
> This is useful, because many applications
>
> - use non-serializable session attributes, so
> it is not possible to simply replicate everything
>
> - do not actually need everything replicated, because they
> can bootstrap all they need from a login context if a filter
> detects, that a failover has happened.
>
> In these cases it can also help to reduce replication traffic a lot.
>
> Unfortunately I stu,bled into some code in StandardSession:
>
> public void setAttribute(String name, Object value, boolean notify) {
> ...
> if ((manager != null)&& manager.getDistributable()&&
> !(value instanceof Serializable))
> throw new IllegalArgumentException
> (sm.getString("standardSession.setAttribute.iae", name));
> ...
> }
>
> This means if you enable "distributable", then you can no longer set any
> non-serializable session attribute. The code is not recent, it goes back
> to at least TC 3.3.
>
> I understand, that it is helpful to devs being informed about
> serialization/replication problems. But I think it is too strict to
> enforce this in StandardSession whch is the base class of all our
> cluster sessions and we always delegate to
> StandardSession.setAttribute() after some cluster specific handling.
>
> The SPEC says:
>
> The container must accept objects that implement the Serializable interface.
> - The container may choose to support storage of other designated
> objects in the
> HttpSession, such as references to Enterprise JavaBeans components and
> transactions.
> - Migration of sessions will be handled by container-specific facilities.
> The distributed servlet container must throw an IllegalArgumentException for
> objects where the container cannot support the mechanism necessary for
> migration
> of the session storing them.
>
> (and some more in 7.7.2).
>
> I think checking for serializability in StandardSession isn't good,
> because AFAIK StandardSession isn't used by any mechanism Tomcat
> supports to implement "distributable".
>
> And in DeltaSession I would like to have the check optional, i.e. only
> check if the configuration wants the attribute to be replicated.
>
> By default all attributes will be replicated as is today, but by
> configuration one will be able to choose attributes to replicate using a
> regexp against the attribute name.
>
> Any remarks?
>
> Rainer
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: dev-unsubscribe@tomcat.apache.org
> For additional commands, e-mail: dev-help@tomcat.apache.org
>
>
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