More reasonable progress with the UnifiedChannelizer. The short version is that I have a pretty major quantity of the server integration tests passing under this new Channelizer. The ones that are failing are typically ones that assert some specific log messages or exception message which may not necessarily apply anymore. I'm still mulling those over.
The basic structure of the UnifiedChannelizer is that it sorta copies the WsAndHttpChannelizer and builds from there, so when this UnfiedChannelizer is configured you'll get HTTP and Websockets. The UnifiedChannelizer gets rid of the entire OpProcessor infrastructure. I think that was a good body of code years ago, but we've now learned quite explicitly what we want Gremlin Server to do and what role it plays. OpProcessor just feels like an unnecessary abstraction now. Removing it simplifies the code of the UnifiedChannelizer, which adds a single UnifiedHandler to the netty pipeline. That UnifiedHandler streamlines all those OpProcessor implementations into one so all the duplicate code is effectively removed by running RequestMessage instances through a single common flow. That means all the request validation, error handling, iterator processing, result building, transaction management, etc. will be in one place. The UnifiedHandler also kills out the GremlinExecutor. That means all the Lifecycle callbacks and random lambdas that generated so much indirection in the name of extensibility are no longer confusing the code base and the wicked hierarchy of timesouts and exception throws are all flattened. When the UnifiedHandler gets a RequestMessage it validates it, builds a Context and creates a Rexster instance (thought i'd bring back the name rather than go with the generic "Worker" interface) that has the Context added to it as a task. The Rexster instance is then submitted to the Gremlin thread pool to do work when a thread is available. Rexster will hang on to that thread awaiting tasks that are assigned to it. For sessionless requests, that means Rexster handles one request and exits. For a sessionful request it means the Rexster will wait for more tasks (Context objects from new requests) to be added to it. The UnifiedHandler holds those Rexster instances in a Map aligning session identifiers to Rexster instances. As Divij alluded to, I suppose this means we are putting down foundation for query cancellation and better insight into the queue of things that are running. Now that the gremlinPool server setting covers both types of requests we no longer have a situation where the number of threads that can be running is unbounded and a "session" will now look a bit like a "long run job" in that it will consume a thread from the pool for as long as the session is open. So if the gremlinPool is 16, you could have 16 sessions active. Sessionless requests would begin to queue as would requests for new sessions and they would be serviced in the order received. I'm still not quite ready for a pull request. Despite having the bulk of the integration tests working, the code isn't quite the way I think it will be finally organized (I used a lot of inner classes and things which probably should change). I also need to figure out how to run the tests. I think I need to run them all per channelizer (old and new) but I think that will push the build time over maximum on Travis, so I may need to break things up somehow. I'm reasonably sure I'll have a branch ready to push before the end of the week. On Mon, Mar 22, 2021 at 5:22 PM Stephen Mallette <[email protected]> wrote: > I've started to play with some ideas for pushing all requests > scripts/bytecode sessions/sessionless down one unified pipeline with one > shared thread pool. The most interesting thing I've seen so far is how much > the code could potentially simplify under this approach. The > GremlinExecutor was the wrong abstraction in a sense and it forced way too > many callbacks as arguments and made error handling kinda sloppy which made > the server code harder to reuse, extend and read. Of course, all that was > built before the first remote graph was built and we were just wildly > guessing at how DS Graph was going to work with all this. Now, I think the > remote model is much more clear, so maybe all this can be made "right" now. > > I think that if I can see any success at all with this in the next few > days, we could include a new UnfiiedChannelizer that would replace the > existing ones. I think we'd keep the old one in place by default and keep > my copy/paste work for SessionOpProcessor that added bytecode there, with > the idea that the UnifiedChannelizer will become the future default as we > get it tested further along the 3.5.x line. > > I imagine I'll have more details on this task tomorrow and will post back > here when I do. > > > On Thu, Mar 18, 2021 at 12:37 PM Divij Vaidya <[email protected]> > wrote: > >> > >> > I suppose the >> > question is how would we ensure that each request for a session ends up >> > being executed on the same thread from the previous request if jobs are >> > randomly submitted to a worker pool? >> >> >> I haven't thought through the details, but on top of my head, we would >> have >> to maintain some request<->thread mapping on the server. This mapping is >> also a building block for a request cancellation feature in future where a >> client would be able to send a cancellation request to the server, the >> server will map the request to a thread executing that request and then >> set >> an interrupt on that thread to signify cancellation. >> >> Divij Vaidya >> >> >> >> On Thu, Mar 18, 2021 at 5:00 PM Stephen Mallette <[email protected]> >> wrote: >> >> > I started a fresh thread for this topic Divij brought up, with more >> > context: >> > >> > > In a scenario where we have both >> > > session-less and sesion-ful requests being made to the server, the >> > resource >> > > allocation will not be fair and may lead to starvation for some >> requests. >> > > This problem exists even today, hence not totally correlated to what >> you >> > > are proposing but I am afraid a wider adoption of explicit >> > > transactions will bring this problem to the spotlight. Hence, we >> should >> > fix >> > > this problem first. A solution would entail converging the worker pool >> > for >> > > both session vs session-less requests. >> > >> > I'm not sure we can get that done in 3.5.0, but maybe? I suppose the >> > question is how would we ensure that each request for a session ends up >> > being executed on the same thread from the previous request if jobs are >> > randomly submitted to a worker pool? >> > >> > >> > On Thu, Mar 18, 2021 at 11:52 AM Divij Vaidya <[email protected]> >> > wrote: >> > >> > > Great idea Stephen. I agree with standardizing the explicit >> transaction >> > > semantics in cases of remote server (implicit aka sessionless is >> already >> > > self explanatory) and unifying the syntax with embedded graph usage. >> > > >> > > Couple of notes: >> > > >> > > 1. I would favor the begin() instead of create() as it's closer to >> > > universally prominent SQL transaction syntax. This would reduce the >> > > learning curve for users of TP. >> > > >> > > 2. From an implementation standpoint, sessionless requests are queued >> on >> > > the server side and are serviced by the worker thread pool. But a >> > > session-ful aka explicit transaction aka managed transaction starts a >> new >> > > single worked thread pool every time. In a scenario where we have both >> > > session-less and sesion-ful requests being made to the server, the >> > resource >> > > allocation will not be fair and may lead to starvation for some >> requests. >> > > This problem exists even today, hence not totally correlated to what >> you >> > > are proposing but I am afraid a wider adoption of explicit >> > > transactions will bring this problem to the spotlight. Hence, we >> should >> > fix >> > > this problem first. A solution would entail converging the worker pool >> > for >> > > both session vs session-less requests. >> > > >> > > 3. You are proposing the idea of having a transaction scoped traversal >> > > object. I agree with it but we need more clarification in behavior wrt >> > the >> > > following scenarios: >> > > >> > > Q. What happens when g.tx().commit() is called on a transaction scoped >> > > traversal object? Does the traversal get closed? >> > > Q. Currently, the same traversal object could be used to execute >> multiple >> > > session-less requests simultaneously in a thread safe manner. Does the >> > same >> > > behaviour apply to transaction scoped traversal? If not, then how do I >> > send >> > > multiple requests in parallel from the client all scoped to the same >> > > transaction on the server? Note that this is different from case of >> multi >> > > threaded transactions because on the server all requests are scoped to >> > > single transaction i.e. single thread but on the client they may be >> > > submitted via multiple threads. >> > > >> > > Regards, >> > > Divij Vaidya >> > > >> > > >> > > >> > > On Thu, Mar 18, 2021 at 4:05 PM Stephen Mallette < >> [email protected]> >> > > wrote: >> > > >> > > > The Transaction object is a bit important with remote cases because >> it >> > > > holds the reference to the session. With embedded use cases we >> > generally >> > > > adhere to ThreadLocal transactions so the Transaction >> implementation in >> > > > that case is more of a controller for the current thread but for >> remote >> > > > cases the Transaction implementation holds a bit of state that can >> > cross >> > > > over threads. In some ways, that makes remote cases feel like a >> > "threaded >> > > > transaction" so that may be familiar to users?? Here's some example >> > > > syntax I currently have working in a test case: >> > > > >> > > > g = traversal().withRemote(conn) >> > > > gtx = g.tx().create() >> > > > assert gtx.isOpen() == true >> > > > gtx.addV('person').iterate() >> > > > gtx.addV('software').iterate() >> > > > gtx.commit() // alternatively you could explicitly rollback() >> > > > assert gtx.isOpen() == false >> > > > >> > > > I hope that documentation changes are enough to unify the syntax and >> > > remove >> > > > confusion despite there still being ThreadLocal transactions as a >> > default >> > > > for embedded cases and something else for remote. At least they will >> > look >> > > > the same, even if you technically don't need to do a g.tx().create() >> > for >> > > > embedded transactions and can just have the control you always had >> with >> > > > g.tx().commit() directly. >> > > > >> > > > Note that the remote Transaction object can support configuration >> via >> > > > onClose(CLOSE_BEHAVIOR) and you could therefore switch from the >> default >> > > of >> > > > "commit on close" to rollback or manual (or i suppose something >> > custom). >> > > > It's nice that this piece works. I don't see a point in supporting >> > > > onReadWrite(READ_WRITE_BEHAVIOR) as it just doesn't make sense in >> > remote >> > > > contexts. >> > > > >> > > > Another point is that I've added what I termed a "Graph Operation" >> > > bytecode >> > > > instances which is bytecode that isn't related to traversal >> > > construction. I >> > > > hope this isn't one of those things where we end up wanting to >> > deprecate >> > > an >> > > > idea as fast as we added it but we needed some way to pass >> > > commit/rollback >> > > > commands and they aren't really part of traversal construction. They >> > are >> > > > operations that execute on the graph itself and I couldn't think of >> how >> > > to >> > > > treat them as traversals nicely, so they sorta just exist as a one >> off. >> > > > Perhaps they will grow in number?? Folks have always asked if >> bytecode >> > > > requests could get "GraphFeature" information - I suppose this could >> > be a >> > > > way to do that?? >> > > > >> > > > Anyway, I will keep going down this general path as it's appearing >> > > > relatively fruitful. >> > > > >> > > > >> > > > >> > > > >> > > > On Thu, Mar 18, 2021 at 6:34 AM Stephen Mallette < >> [email protected] >> > > >> > > > wrote: >> > > > >> > > > > > We should just communicate clearly that a simple remote >> traversal >> > > > > already uses a transaction by default, >> > > > > >> > > > > That's a good point because even with this change we still have a >> > > > > situation where a single iterated remote traversal will generally >> > mean >> > > a >> > > > > server managed commit/rollback, but in embedded mode, we have an >> open >> > > > > transaction (for transaction enabled graphs - TinkerGraph will >> behave >> > > > more >> > > > > like a remote traversal, so more confusion there i guess). I'm not >> > sure >> > > > how >> > > > > to rectify that at this time except by way of documentation. >> > > > > >> > > > > The only thing I can think of is that the default for embedded >> would >> > > have >> > > > > to be auto-commit per traversal. In that way it would work like >> > remote >> > > > > traversals and for graphs that don't support transactions like >> > > > TinkerGraph. >> > > > > Of course, that's the kind of change that will break a lot of >> code. >> > > Maybe >> > > > > we just keep that idea for another version. >> > > > > >> > > > > On Thu, Mar 18, 2021 at 4:21 AM <[email protected]> wrote: >> > > > > >> > > > >> I like the idea of adding transactions for remote traversals as >> they >> > > > >> close a gap in functionality that we currently have for remote >> > > > traversals. >> > > > >> We should just communicate clearly that a simple remote traversal >> > > > already >> > > > >> uses a transaction by default, meaning that the server will roll >> > back >> > > > any >> > > > >> changes if any exception occurs. Users often ask about how to do >> > > > >> transactions with a remote traversal because they don't know >> about >> > > this >> > > > and >> > > > >> I'm afraid that we might add even more confusion if we now add >> > > > transactions >> > > > >> for remote traversals. Hence why I think that we should >> communicate >> > > this >> > > > >> clearly when we add remote transactions. >> > > > >> >> > > > >> Getting this to work in the GLVs should be possible but will >> require >> > > > some >> > > > >> effort. I think we would have to introduce some >> > > > >> "DriverRemoteTransactionTraversal" that doesn't submit the >> traversal >> > > on >> > > > a >> > > > >> terminal step but saves it and then submits all saved traversals >> > > > together >> > > > >> on close(). >> > > > >> This also means that we should directly add an async version of >> > > close(), >> > > > >> maybe closeAsync()? (Same for commit() and rollback()) >> > > > >> >> > > > >> I also like create() better than traversal() because it would >> > confuse >> > > me >> > > > >> to first start a traversal with traversal() and then also start a >> > > > >> transaction with the same method. >> > > > >> >> > > > >> -----Ursprüngliche Nachricht----- >> > > > >> Von: Stephen Mallette <[email protected]> >> > > > >> Gesendet: Donnerstag, 18. März 2021 00:01 >> > > > >> An: [email protected] >> > > > >> Betreff: Re: [DSISCUSS] Remote Transactions >> > > > >> >> > > > >> One thing I should have noted about tx().create(). The create() >> very >> > > > well >> > > > >> could have been named traversal(), thus the previous example >> reading >> > > as: >> > > > >> >> > > > >> g = traversal().withEmbedded(graph) >> > > > >> // or >> > > > >> g = traversal().withRemote(conn) >> > > > >> gtx = g.tx().traversal() >> > > > >> gtx.addV('person').iterate() >> > > > >> gtx.addV('software').iterate() >> > > > >> gtx.close() // alternatively you could explicitly commit() or >> > > rollback() >> > > > >> >> > > > >> You're basically spawning a new GraphTraversalSource from the >> > > > Transaction >> > > > >> object rather than from a Graph or AnonymousTraversal. I chose >> > > create() >> > > > >> because it felt like this looked weird: >> > > > >> >> > > > >> g = traversal().withRemote(conn).tx().traversal() >> > > > >> >> > > > >> which would be a weird thing to do I guess, but just seeing >> > > > "traversal()" >> > > > >> over and over seemed odd looking and I wanted to differentiate >> with >> > > the >> > > > >> Transaction object even though the methods are identical in what >> > they >> > > > do. I >> > > > >> suppose I also drew inspiration from: >> > > > >> >> > > > >> Transaction.createdThreadedTx() >> > > > >> >> > > > >> which I think we might consider deprecating. JanusGraph would >> simply >> > > > >> expose their own Transaction object in the future that has that >> > method >> > > > as I >> > > > >> imagine folks still use that feature. As far as I know, no other >> > graph >> > > > >> implements that functionality and my guess is that no one will >> > likely >> > > > do so >> > > > >> in the future. >> > > > >> >> > > > >> anyway, if you like traversal() better than create() or the other >> > way >> > > > >> around, please let me know >> > > > >> >> > > > >> On Wed, Mar 17, 2021 at 5:33 PM David Bechberger < >> > [email protected] >> > > > >> > > > >> wrote: >> > > > >> >> > > > >> > I am in favor of this change as I any idea that unifies the >> > multiple >> > > > >> > different ways things work in TP will only make it easier to >> learn >> > > and >> > > > >> > adopt. >> > > > >> > >> > > > >> > I don't know that I have enough knowledge of the inner >> workings of >> > > > >> > transactions to know what/if this will cause problems. >> > > > >> > >> > > > >> > Dave >> > > > >> > >> > > > >> > On Wed, Mar 17, 2021 at 12:57 PM Stephen Mallette >> > > > >> > <[email protected]> >> > > > >> > wrote: >> > > > >> > >> > > > >> > > We haven't touched "transactions" since TP3 was originally >> > > designed. >> > > > >> > > They have remained a feature for embedded use cases even in >> the >> > > face >> > > > >> > > of the >> > > > >> > rise >> > > > >> > > of remote graph use cases and result in major inconsistencies >> > that >> > > > >> > > really bother users. >> > > > >> > > >> > > > >> > > As we close on 3.5.0, I figured that perhaps there was a >> chance >> > to >> > > > >> > > do something radical about transactions. Basically, I'd like >> > > > >> > > transactions to work irrespective of remote or embedded usage >> > and >> > > > >> > > for them to have the >> > > > >> > same >> > > > >> > > API when doing so. In mulling it over for the last day or so >> I >> > > had a >> > > > >> > > realization that makes me believe that the following is >> > possible: >> > > > >> > > >> > > > >> > > g = traversal().withEmbedded(graph) >> > > > >> > > // or >> > > > >> > > g = traversal().withRemote(conn) >> > > > >> > > gtx = g.tx().create() >> > > > >> > > gtx.addV('person').iterate() >> > > > >> > > gtx.addV('software').iterate() >> > > > >> > > gtx.close() // alternatively you could explicitly commit() or >> > > > >> > > rollback() >> > > > >> > > >> > > > >> > > // you could still use g for sessionless, but gtx is "done" >> > after >> > > // >> > > > >> > > you close so you will need to create() a new gtx instance >> for a >> > // >> > > > >> > > fresh transaction assert 2 == g.V().count().next() >> > > > >> > > >> > > > >> > > Note that the create() method on tx() is the new bit of >> > necessary >> > > > >> syntax. >> > > > >> > > Technically, it is a do-nothing for embedded mode (and you >> could >> > > > >> > > skip it for thread-local auto-transactions) but all the >> > > > >> > > documentation can be shifted so that the API is identical to >> > > remote. >> > > > >> > > The change would be non-breaking as the embedded transaction >> > > > >> > > approach would remain as it is, but would no longer be >> > documented >> > > as >> > > > >> > > the preferred approach. Perhaps we could one day disallow it >> but >> > > > >> > > it's a bit of a tangle of ThreadLocal that I'm not sure we >> want >> > to >> > > > >> touch in TP3. >> > > > >> > > >> > > > >> > > What happens behind the scenes of g.tx().create() is that in >> > > remote >> > > > >> > > cases the RemoteConnection constructs a remote Transaction >> > > > >> > > implementation which basically is used to spawn new traversal >> > > source >> > > > >> > > instances with a session based connections. The remote >> > Transaction >> > > > >> > > object can't support >> > > > >> > transaction >> > > > >> > > listeners or special read-write/close configurations, but I >> > don't >> > > > >> > > think that's a problem as those things don't make a lot of >> sense >> > > in >> > > > >> > > remote use cases. >> > > > >> > > >> > > > >> > > From the server perspective, this change would also mean that >> > > > >> > > sessions would have to accept bytecode and not just scripts, >> > which >> > > > >> > > technically shouldn't be a problem. >> > > > >> > > >> > > > >> > > One downside at the moment is that i'm thinking mostly in >> Java >> > at >> > > > >> > > the moment. I'm not sure how this all works in other variants >> > just >> > > > >> > > yet, but >> > > > >> > I'd >> > > > >> > > hope to keep similar syntax. >> > > > >> > > >> > > > >> > > I will keep experimenting tomorrow. If you have any thoughts >> on >> > > the >> > > > >> > matter, >> > > > >> > > I'd be happy to hear them. Thanks! >> > > > >> > > >> > > > >> > >> > > > >> >> > > > >> >> > > > >> > > >> > >> >
