[jbosscache-dev] migrating data stored in 1.x format to VAM format
Mircea Markus
mircea.markus at gmail.com
Mon Mar 5 17:07:14 EST 2007
Hi,
On start the root node is created with an empty map. I've changed it to be
created with a sql null value rather than an empty map.
This way we'll stay consistent with the nodes added indirectly(as they are
parents of nodes that are specifically added).
I also hope this will solve extending JDBCacheLoader problem, as I think
that for deserializaion the TransformingJDBCCacheLoader knows how to handle
DB nulls.
Cheers,
Mircea
On 3/4/07, Galder Zamarreno < galder.zamarreno at redhat.com > wrote:
>
> I've got this working, including some basic unit tests and manual
> examples to transform entired cache stores from 1.x data to 2.x. These
> last manual examples include source code, 1.x cache stores (file and
> jdbc derby db) and sample cache configurations.
>
> Apart from the MV issue referred earlier, I have realised that
> TransformingJDBCCacheLoader will have to extend JDBCCacheLoaderOld
> instead of JDBCCacheLoader.
>
> The reason is because when JDBCCacheLoader starts, if the root does not
> exist, it'll create it, which in the TransformingJDBCCacheLoader will
> mean creating it in 2.x format.
>
> This wouldn't be a problem if the root node didn't need querying again,
> but if customers want to migrate their data, they will start looping
> from the node (cache.getRoot ()) and the first thing they'll get its
> children. This results in trying to load the root node from the cache
> store which breaks, as we're reading from db in 1.x format.
>
> Remember that the TransformingJDBCCacheLoader reads in 1.x format and
> stores in 2.x format.
>
> This has a very easy resolution which is extending JDBCCacheLoaderOld.
> After that, it works like a treat :).
>
> Manik, assuming you're happy with the original idea, would extending
> JDBCCacheLoaderOld for this one off cache loader be ok with you?
>
> Galder Zamarreno wrote:
> > I haven't touched this issue for a couple of weeks and over the last
> > couple of days I had the chance to get back into it.
> >
> > After discussions with Brian we came up with a different approach for
> this.
> >
> > My previous approach (don't need to read all below) relied on
> > introducing legacy code into the main source code that would be able to
> > read 1.x serialization. As I started doing it, I realised that it would
> > need a lot of changes and it would clutter the 2.0 codebase.
> >
> > Instead, with the help of Brian, we came up with a different idea, which
>
> > is creating two one-off cache loaders, TransformingJDBCCacheLoader and
> > TransformingFileCacheLoader. They extend the existing cache loaders, but
> > they differentiate by unmarshall stuff in the 1.x way.
> >
> > This way, we have cache loaders that can read in 1.x way and write in
> > 2.x way. Now, a customer just needs to write a program that uses a cache
> > configured to use any of these two cache loaders above and all it has to
>
> > do is loop through the tree reading all nodes and putting them back, and
> > voila! you have your data store format changed (I'll be writing an
> > example of this).
> >
> > It's a pretty clean solution to transforming data without making changes
>
> > to main o.j.cache tree.
> >
> > But, there's always a but :), 1.4.x used
> > org.jboss.invocation.MarshalledValue so there's no way of getting around
> > the need of having this class to do this. This is because
> > JDBCCacheLoader stored instances of MarshalledValue, so even the MV
> > class in AOP would not work cos it's a different package (it'd result in
> > CCE)
> >
> > One thing Brian suggested is that these two cache loaders and
> > jboss-minimal are kept in a separate dir structure to the main one and
> > when we distribute, we provide an extra jar containing these that can be
> > used to transform data and that's it. After that, you get rid of it, you
>
> > go back to the standard libraries.
> >
> > It's pretty hard to find a neater way of dealing with this but the
> > benefits are worth it, customer's data stays alive!
> >
> > Manik and the rest, thoughts?
> >
> > Galder Zamarreno wrote:
> > > Manik Surtani wrote:
> > >> On 5 Feb 2007, at 19:57, Galder Zamarreno wrote:
> > >>
> > >>> Quick (but a bit lengthy :( ) update on this:
> > >>>
> > >>> - I've created a new Marshaller called Legacy1xMarshaller (anyone's
> > >>> got a better name?) which extends o.j.c.m.AsbtractMarshaller that
> > >>> would do the job of marshalling stuff in the 1.x fashion. This is
> to
> > >>> be used by JDBCCacheLoader and FileCacheLoader if configured to use
> > >>> 1.x marshalling. This has the benefit that the code in these cache
> > >>> loaders only have to do getMarshaller().whatever... , making it
> very
> > >>> simple to switch from VAM to Legacy Marshaller.
> > >>
> > >> I presume the VAM would transparently flip between marshallers,
> based
> > >> on the version short at the head of the stream?
> > >
> > > The problem is that 1.x marshalling for cache loaders did not have
> > > version numbers at the start, it was plain java serialization. Can
> you
> > > expect VAM to detect that? That's why I thought of a Marshaller
> instance
> > > in AbstractCacheLoader that would either use VAM or the Legacy one.
> We
> > > could however assume that if VAM does not find version number, it
> tries
> > > to use Legacy one.
> > >
> > > As you said later in the email, it seems like 1.4.x dealt with this
> > > similar situation. I'll look at it.
> > >
> > >>
> > >>>
> > >>> - In order to do this, I need to add a new method to
> > >>> o.j.c.m.Marshaller called objectToStream(OutputStream). The reason
> > >>> for doing is so that FileCacheLoader just needs to call
> > >>> getMarshaller().objectToStream() when it's trying to store data.
> This
> > >>> will avoid having an if statement in storeAttributes() checking
> which
> > >>> Marshaller is used, and calling objectToObjectStream with the
> > >>> corresponding ObjectOutpuStream.
> > >>
> > >> Again, isn't this already in the VAM?
> > >
> > > Not for OutputStream. You have objectToObjectStream(Object obj,
> > > ObjectOutputStream out) and objectFromStream(InputStream is), but not
>
> > > objectToStream for OutputStreams such as FileOutputStream.
> > >
> > >>
> > >>>
> > >>> - The decision maker for which Marshaller to use is to be done in
> > >>> AbstractCacheLoader which will store the Marshaller used by
> > >>> CacheLoader. getMarshaller() would decide upon configuration, which
> > >>> Marshaller to use, whether the default cache.getMarshaller() which
> is
> > >>> VAM or the legacy one, making it quite clean to switch from to
> > another.
> > >>
> > >> Look at the VAM in the 1.4.x tree - it deals with "legacy support"
> to
> > >> deal with JBC 1.2.x and 1.3.x for RPC calls. (removed in 2.x since
> > >> the legacy support was no longer needed). Could easily be
> > >> re-introduced if needed to supportr legacy marshalling for CLs.
> > >
> > > Ok, i'll definitely have a look at that.
> > >
> > >>
> > >>>
> > >>> - Configuration wise, I created
> Legacy1xMarshallingCacheLoaderConfig
> > >>> (I couldn't come up with a better name!) which extends
> > >>> IndividualCacheLoaderConfig. JDBCCacheLoaderConfig and
> > >>> FileCacheLoaderConfig will extend
> > >>> Legacy1xMarshallingCacheLoaderConfig instead.
> > >>
> > >> Could drop the 1x in the name, I suppose? :-)
> > >
> > > No probs :)
> > >
> > >>
> > >>>
> > >>> - Inside Legacy1xMarshallingCacheLoaderConfig, I search for
> > >>> cache.loader.marshalling.1.x (name again!) boolean property in the
> > >>> <properties> section. If true, it uses legacy marshalling, and if
> > >>> false, which is default value, VAM.
> > >>>
> > >>> - I have extended CacheLoaderTestsBase to create
> > >>> FileCacheLoaderLegacyMarshallingTest which tests the
> FileCacheLoader
> > >>> with legacy marshalling. I'll be doing the same for
> JDBCCacheLoader.
> > >>>
> > >>> - Finally and one of the most important aspects, previous
> marhalling
> > >>> relies on these classes:
> > >>>
> > >>> org.jboss.invocation.MarshalledValue ;
> > >>> org.jboss.invocation.MarshalledValueInputStream;
> > >>>
> > >>> Which used to be located in jboss-minimal.jar in 1.x. There's v
> > >>> similar classes in AOP but not the same, so I'm gonna be creating a
>
> > >>> legacy directory in lib with this library. To avoid compile time
> > >>> dependency, Legacy1xMarshaller will be instantiated via reflection,
> > >>> so only people who actually use this will need this library. The
> > >>> library has no conflicts with existing 2.x libraries.
> > >>
> > >> Look at the jboss-common-core jar and particularly JBCOMMON-8 in
> JIRA.
> > >>
> > >
> > > So, did you test whether you could read data written with
> > > JDBCCacheLoader wiht MV classes with a JDBCCacheLoader not using MV
> > > classes? That's one of the tests I wanted to do to see whether this
> > > classes were necessary.
> > >
> > > jboss-common-core.jar contains MarshalledValueOutputStream and
> > > MarshalledValueInputStream so that wouldn't be a problem for FCL.
> > > JDBCCacheLoader on the contrary, wrapped the node in MarshalledValue
> and
> > > the wrote it as an ObjectOutputStream. I'll look at the commons code
> to
> > > see whether it's the same which I guess might be.
> > >
> > > There's a MarshalledValue in aop libraries but quick glance at the
> code
> > > showed that it's slightly different.
> > >
> > >>>
> > >>> The last problem is that these two classes access
> > >>> org.jboss.logging.Logger that used to be in jboss-common.jar. Now
> > >>> this jar certainly classes with jboss-common-core.jar in 2.x, so
> > >>> what's I've done is get jboss-logging-spi.jar 2.0.2.GA and put it
> in
> > >>> the legacy directory.
> > >>>
> > >>> So, we end up having two legacy libraries in lib/legacy but they're
> > >>> only needed at runtime if using 1.x marhalling. I guess it's the
> > >>> price to pay to make customer's life a bit easier.
> > >>>
> > >>
> > >> Trying to avoid a legacy jar dir ... like I said, see if the MV and
> > >> MVIS can be in jboss-common-core (without JBoss Logging deps!)
> > >
> > > Yeah defo, we wanna avoid any legacy jars.
> > >
> > >>
> > >>> The other alternative would be for 1.x marshaller not to use this
> > >>> org.jboss.invocation.* classes and just write to Object streams but
> I
> > >>> think these classes have an impact in the format of the marshalled
> > >>> data. Brian, do you know a bit more about the role of these
> classes?
> > >>>
> > >>> A bit more complicated than initially expected but I can't see any
> > >>> easier way of providing backwards compatibility. Hopefully we
> should
> > >>> be able to phase it out asap, 3.x? :)
> > >>>
> > >>> What this has shown as well is how different CacheLoaders
> marshalled
> > >>> things in a slightly different way which makes having a common
> > >>> framework for this even more necessary, i.e. VAM. :D
> > >>>
> > >>> Hope you're not snoring by now ;)
> > >>>
> > >>> If you have better ideas for the naming I used, speak up :)
> > >>>
> > >>> Galder Zamarre�o
> > >>> Sr. Software Maintenance Engineer
> > >>> JBoss, a division of Red Hat
> > >>>
> > >>> -----Original Message-----
> > >>> From: jbosscache-dev-bounces at lists.jboss.org
> > >>> [mailto: jbosscache-dev-bounces at lists.jboss.org ] On Behalf Of
> Galder
> > >>> Zamarreno
> > >>> Sent: 31 January 2007 01:01
> > >>> To: Manik Surtani
> > >>> Cc: jbosscache-dev at lists.jboss.org
> > >>> Subject: RE: [jbosscache-dev] migrating data stored in 1.x format
> to
> > >>> VAM format
> > >>>
> > >>> +1, VAM should be the default.
> > >>>
> > >>> Only people who are resilient to change their existing stores to
> VAM
> > >>> should use the 1.x option, which would need explicitly definition.
> > >>>
> > >>> Galder Zamarre�o
> > >>> Sr. Software Maintenance Engineer
> > >>> JBoss, a division of Red Hat
> > >>>
> > >>>
> > >>> -----Original Message-----
> > >>> From: Manik Surtani [mailto:manik at jboss.org]
> > >>> Sent: 30 January 2007 22:55
> > >>> To: Galder Zamarreno
> > >>> Cc: jbosscache-dev at lists.jboss.org
> > >>> Subject: Re: [jbosscache-dev] migrating data stored in 1.x format
> to
> > >>> VAM format
> > >>>
> > >>> I see what you mean, although I would like the default to be to use
> > >>> the VAM.
> > >>>
> > >>> --
> > >>> Manik Surtani
> > >>>
> > >>> Lead, JBoss Cache
> > >>> JBoss, a division of Red Hat
> > >>>
> > >>> Email: manik at jboss.org
> > >>> Telephone: +44 7786 702 706
> > >>> MSN: manik at surtani.org
> > >>> Yahoo/AIM/Skype: maniksurtani
> > >>>
> > >>>
> > >>>
> > >>> On 30 Jan 2007, at 20:45, Galder Zamarreno wrote:
> > >>>
> > >>>> Actually, the more I think about this, the less I like the idea of
> > >>>> switching the marshalling from 1.x to 2.x at the CacheLoaders
> > >>>> level, or at least forcing them to do so.
> > >>>>
> > >>>> Customers that want to use JBossCache 2.x might be reluctant to
> > >>>> migrate their data from one format to the other. I can see how an
> > >>>> existing customer might think this is a proper pain in the ass,
> > >>>> independent of the benefits, and might reduce adoption among them.
> > >>>>
> > >>>> We want to remove barriers upgrading, but at the same time, we
> want
> > >>>> new customer to use new marshalling, so I'd actually implement the
>
> > >>>> possibility to use 1.x marshalling which is plan java
> serialization
> > >>>> at the CacheLoader level. This could easily achieved adding a
> > >>>> property to the <properties> section.
> > >>>>
> > >>>> Just note that this does not apply to the marshalling done at
> > >>>> replication level as there's no hard data that needs migrating.
> > >>>>
> > >>>> Galder Zamarre�o
> > >>>> Sr. Software Maintenance Engineer
> > >>>> JBoss, a division of Red Hat
> > >>>>
> > >>>> -----Original Message-----
> > >>>> From: jbosscache-dev-bounces at lists.jboss.org [mailto:jbosscache-dev-
> > >>>> bounces at lists.jboss.org] On Behalf Of Galder Zamarreno
> > >>>> Sent: 25 January 2007 13:07
> > >>>> To: jbosscache-dev at lists.jboss.org
> > >>>> Subject: [jbosscache-dev] migrating data stored in 1.x format to
> > >>>> VAM format
> > >>>>
> > >>>> Hi all,
> > >>>>
> > >>>> I'm deferring http://jira.jboss.com/jira/browse/JBCACHE-879 to
> > >>>> BETA2 because I still need to write this: http://jira.jboss.com/
> > >>>> jira/browse/JBCACHE-882
> > >>>>
> > >>>> The reason I'm deferring it is because I can't see a
> > >>>> straightforward way of doing such thing right now. Ideally, you
> > >>>> should be able run a 1.x version (cache1) and a 2.x version
> > >>>> (cache2) of JBC in the same VM so that you can do a loop of
> > >>>> cache1.get() and call cache2.put(). However, I have doubts that
> > >>>> that this approach will be free of class loading issues. What do
> > >>>> you think?
> > >>>>
> > >>>> I was wondering whether Region based could help here, but I can't
> > >>>> see right now how this could be done.
> > >>>>
> > >>>> Something I had in mind is having the capability of to start a
> > >>>> cache with either 1.x marshalling or VAM marshalling, but oriented
> > >>>> at being used only at the cache loader level. It wouldn't make
> much
> > >>>> sense for replication because there's no hard data there.
> > >>>>
> > >>>>
> > >>>> I thought that you could start two instances of cache 2.x, first
> > >>>> with 1.x. marshalling and the other one with VAM both pointing to
> > >>>> different JDBCCacheLoader stores. You could then get from the
> first
> > >>>> using normal mmarshalling and put in the second one which has VAM
> > >>>> marshalling active, what do you think?
> > >>>>
> > >>>> If you like the approach, I should be have it ready by BETA2.
> > >>>>
> > >>>> This last approach looks simpler to me, what do you think?
> > >>>>
> > >>>> Galder Zamarre�o
> > >>>> Sr. Software Maintenance Engineer
> > >>>> JBoss, a division of Red Hat
> > >>>>
> > >>>>
> > >>>>
> > >>>> _______________________________________________
> > >>>> jbosscache-dev mailing list
> > >>>> jbosscache-dev at lists.jboss.org
> > >>>> https://lists.jboss.org/mailman/listinfo/jbosscache-dev
> > >>>>
> > >>>> _______________________________________________
> > >>>> jbosscache-dev mailing list
> > >>>> jbosscache-dev at lists.jboss.org
> > >>>> https://lists.jboss.org/mailman/listinfo/jbosscache-dev
> > >>>
> > >>>
> > >>>
> > >>> _______________________________________________
> > >>> jbosscache-dev mailing list
> > >>> jbosscache-dev at lists.jboss.org
> > >>> https://lists.jboss.org/mailman/listinfo/jbosscache-dev
> > >>
> > >
> > >
> >
>
> --
> Galder Zamarre�o
> Sr. Software Maintenance Engineer
> JBoss, a division of Red Hat
>
> _______________________________________________
> jbosscache-dev mailing list
> jbosscache-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/jbosscache-dev
>
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