Great initiative. Instead of storing such information in a plain-text file it could be stored in the neo4j store itself (as a sub-reference node or something).
I don't know if that'd be good/better though. 2010/1/4 Tobias Ivarsson <[email protected]>: > Hi, > > Neo4j today is made up of a core service that persists nodes, relationships > and properties. In addition to that there are a number of additional > services, where index-util is probably the most used and most important at > the moment. index-util is also a good example of the problem I would like to > discuss in this email. > > With the current architecture there is no way of introspecting which > additional services have been initialized with a particular Neo store, for > example there is no way of telling which (if any) IndexService has been > used. This causes problems with the transaction recovery process, where the > recovery mechanism today has to know about all possible extension services > without having a compile time dependency on them. Needless to say this > causes a mess. The code for this is ugly and borderline-buggy. It also > causes a problem when introspecting a store, or even restarting your > software, since it is up to the programmer to remember to restart all of the > same services as last time. > > I would like to propose an addition to the store, in a separate metadata > file in the store directory, where we store a simple list of all started > additional services. Does anyone have any suggestions to what this should > look like to be reasonable future proof (i.e. be able to handle some service > that is not implemented yet as well as the current index-utils). > > What comes to mind is something similar to the Java ServiceLoader API [1], > but simplified with the fact that we can require all classes referenced in > the file to implement one specific interface, and we know where the file > will be, in effect taking out all the complications involving ClassLoaders. > What I'm worrying about is that storing Java classnames in a file will make > this metadata unusable to any future implementations of the NeoStore format > outside of the Java platform. Any suggestions to how information about > loaded services can be stored is welcome, my idea of a clear text file might > not even be good (since people have a tendency to think they can patch those > manually). > > Since we have a community of smart and entrepreneurial individuals I thought > I'd throw the question out here and see if I got any good responses. > > Cheers, > Tobias > > [1] http://java.sun.com/javase/6/docs/api/java/util/ServiceLoader.html > Simple explanation of how it works: > * You have an interface with fully qualified classname: > com.somedomain.someproduct.ServiceInterface > * In each jar that provides implementations of the ServiceInterface you add > a file called > META-INF/services/com.somedomain.someproduct.ServiceInterface > * In this file you put the fully qualified classnames of each implementing > class separated by newline > * In your code you do: ServiceLoader<ServiceInterface> impls = > ServiceLoader.load(ServiceInterface.class); > -- > Tobias Ivarsson <[email protected]> > Hacker, Neo Technology > www.neotechnology.com > Cellphone: +46 706 534857 > _______________________________________________ > Neo mailing list > [email protected] > https://lists.neo4j.org/mailman/listinfo/user > -- Mattias Persson, [[email protected]] Neo Technology, www.neotechnology.com _______________________________________________ Neo mailing list [email protected] https://lists.neo4j.org/mailman/listinfo/user
