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https://issues.apache.org/jira/browse/JENA-624?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15033730#comment-15033730
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Andy Seaborne commented on JENA-624:
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Re: lock exposure:
This is more about style.
I think it would be better to have a private lock for the object's transaction
control, not a public one.
An application may be using the dataset lock itself for other purposes so (1)
the policy of MR+SW may be unexpected and (2) a bug in the application may
overcall {{leaveCriticalSection}} and this would not be caught but it would
break the system. This is analogous to {{synchronized}} methods exposing the
objects mutex.
Just one of many:
http://stackoverflow.com/questions/416183/in-java-critical-sections-what-should-i-synchronize-on#416198
Digressing a bit:
While {{DatasetGraphInMemory}} is one-thread/one-transaction, other systems do
allow (if you get very complicated) multiple threads per transaction prodiving
within the transaction, MRSW applies.
This will get hard in Fuseki if/when multi-request transactions get done. A
better transaction coordinator will make that easier: e.g. [mantis
TransactionCoordinator|https://github.com/afs/mantis/blob/master/dboe-transaction/src/main/java/org/seaborne/dboe/transaction/txn/TransactionCoordinator.java]
but I'm not sure its all the way there yet.
> Develop a new in-memory RDF Dataset implementation
> --------------------------------------------------
>
> Key: JENA-624
> URL: https://issues.apache.org/jira/browse/JENA-624
> Project: Apache Jena
> Issue Type: Improvement
> Reporter: Andy Seaborne
> Assignee: A. Soroka
> Labels: java, linked_data, rdf
>
> The current (Jan 2014) Jena in-memory dataset uses a general purpose
> container that works for any storage technology for graphs together with
> in-memory graphs.
> This project would develop a new implementation design specifically for RDF
> datasets (triples and quads) and efficient SPARQL execution, for example,
> using multi-core parallel operations and/or multi-version concurrent
> datastructures to maximise true parallel operation.
> This is a system project suitable for someone interested in datatbase
> implementation, datastructure design and implementation, operating systems or
> distributed systems.
> Note that TDB can operate in-memory using a simulated disk with
> copy-in/copy-out semantics for disk-level operations. It is for faithful
> testing TDB infrastructure and is not designed performance, general in-memory
> use or use at scale. While lesson may be learnt from that system, TDB
> in-memory is not the answer here.
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