Since RemoteGraph is used on the client to connect to a remote graph
database, I think its fine to have a tight coupling between the binding and
the traversal source, since that allows for binding reuse when multiple
queries are issued in one session. As such, one would instantiate a
traversal source with binding for each session which would make it
threadsafe.
I would strongly argue in favor of clearing the bindings after a traversal
is compiled/executed in order to avoid accidental binding reuse between
requests. It's better to throw an exception saying that a particular
binding is missing then to reuse one and have the user figure out why the
result set is strange imho.
On Wed, Jul 13, 2016 at 3:11 PM Marko Rodriguez <okramma...@gmail.com>
wrote:
> Hello,
>
> ScriptEngine’s prefer to have compile scripts with bindings as a compiled
> script will execute much faster than one that needs to be compiled. Thus,
> for a traversal that will be run over and over again, but with for instance
> different g.V(id) sources, its all about using ScriptEngine bindings. How
> do we support bindings in a language agnostic way?
>
> The big problem is Java. The GraphTraversal API is strongly typed and
> thus, we can’t simply do stuff like g.V(bind(“id”,2)). Or can we?
>
>
> b = new Bindings();
> g = graph.traversal().withBindings(b);
> g.V(b.of(“id”,2)).out(“created”).values(“name”)
>
>
> What is this all about?
>
> When you do b.of(“id”,2), it returns 2 (Java API is happy). However, the
> underlying Bytecode will know when a new argument has been passed to it. It
> will ask Bindings, "was a binding for 2 just added?" If so, then the
> Bytecode rewrites itself such that the argument is binding(“id”,2).
>
> Then, when the traversal is sent to GremlinServer to be evaluated (lets
> say via Gremlin-Groovy), the Bytecode translator will make the Groovy
> String script look as:
>
> g.V(id).out(“created”).values(“name”)
>
>
> And it will have JSR223 ScriptEngine bindings of {id:2}.
>
>
> https://github.com/apache/tinkerpop/blob/TINKERPOP-1278/gremlin-groovy/src/main/java/org/apache/tinkerpop/gremlin/java/translator/GroovyTranslator.java
>
> Thus, TinkerPop Bindings become a first class citizen in Gremlin. Next,
> what about when Gremlin-Java is translating Bytecode. Well, Java doesn’t
> care about script compilation speed as its Bytecode translator doesn’t
> generate a String, but a Traversal via reflection.
>
>
> https://github.com/apache/tinkerpop/blob/TINKERPOP-1278/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/util/JavaTranslator.java
>
> If JavaTranslator sees a binding in the Bytecode is ignores the binding
> key, and only uses its value:
>
> g.V(2).out(“created”).values(“name”)
>
>
> So this can get awkward for users. However, we can make bindings reusable.
>
> b = new Bindings();
> g = graph.traversal().withBindings(b);
> g.V(b.of(“id”,2)).out(“created”).values(“name”)
> b.clear()
> g.V().out(b.of(“a”,”knows”))
> b.clear()
>
> In fact, it would be possible to automatically reset the bindings every
> time a traversal is compiled. Thus,
>
> b = new Bindings();
> g = graph.traversal().withBindings(b);
> g.V(b.of(“id”,2)).out(“created”).values(“name”)
> g.V().out(b.of(“a”,”knows”))
>
>
> Now, you may say — “well, aren’t traversal sources suppose to be thread
> safe.” To that I say: “yes and if you do it like this, you can only execute
> one traversal at a time.” If you want thread safety:
>
>
> g = graph.traversal();
> b = new Bindings();
> g.withBindings(b).V(b.of(“id”,2)).out(“created”).values(“name”)
> g.withBindings(b).V().out(b.of(“a”,”knows”))
>
>
> For most people, they will have a RemoteGraph traversal source and not
> worry about thread safety here. On GremlinServer, thread safety isn’t an
> issue as withBindings() is a TraversalSource step and thus, part of the
> Bytecode reconstructed at compile time.
>
> Anywho, that is the best I could come up with that will work for Java,
> Groovy, and Python. Unfortunately Java (and Groovy) are statically typed so
> we have to work around this.
>
> Thoughts?,
> Marko.
>
> http://markorodriguez.com
>
>
>
>
