On 19 February 2014 07:12, Galder Zamarreño <gal...@redhat.com> wrote: > > On 03 Feb 2014, at 19:01, Dan Berindei <dan.berin...@gmail.com> wrote: > >> >> >> >> On Mon, Feb 3, 2014 at 6:28 PM, Radim Vansa <rva...@redhat.com> wrote: >> >>>> For sync we would want to invoke directly to avoid context switching. >> >>> I think you haven't properly understood what I was talking about: the >> >>> putAsync should not switch context at all in the ideal design. It should >> >>> traverse through the interceptors all the way down (logically, in >> >>> current behaviour), invoke JGroups async API and jump out. Then, as soon >> >>> as the response is received, the thread which delivered it should >> >>> traverse the interceptor stack up (again, logically), and fire the >> >>> future. >> > A Future doesn't make much sense with an async transport. The problem >> > is with an async transport you never get back a response so you never >> > know when the actual command is completed and thus a Future is >> > worthless. The caller wouldn't know if they could rely on the use of >> > the Future or not. >> >> You're right, there's one important difference between putAsync and put >> with async transport: in the first case you can find out when the >> request is completed while you cannot with the latter. Not requiring the >> ack can be an important optimization. I think that both versions are >> very valid: first mostly for bulk operations = reduction of latency, >> second for modifications that are acceptable to fail without handling that. >> I had the first case in my mind when talking about async operations, and >> there the futures are necessary. >> >> A couple more differences: >> 1. You can't do commitAsync(), but you can configure the commit to be >> replicated asynchronously (1PC). Although we did talk about removing that >> option... >> 2. If you do putAsync(k, v1); putAsync(k, v2), there is no ordering between >> the two and you might end up with k=v1 in the cache. > > If there’s any relationship between both puts for the caller thread, the > caller must make sure that the second put is only called after the first has > completed.
Actually in such a case I would strongly expect Infinispan to keep the two operations in order. This is not to be pushed on user's responsibility. > > If there’s separate threads calling it and it relies on this, it should call > replace the second time, i.e. replaceAsync(k, v1, v2) to get the guarantees > it wants. > > What is really important is that the order in which they are executed in one > node/replica is the same order in which they’re executed in all other nodes. > This was something that was not maintained when async marshalling was enabled. +1000 But also I'd stress that any sync operation should have a Future returned, someone in this long thread suggested to have an option to drop it for example to speedup bulk imports, but I really can't see a scenario in which I wouldn't want to know about a failure. Let's not do the same mistake that made MongoDB so "popular" ;-) Bulk imports can still be mad efficient without strictly needing to go these lenghts. Sanne > >> >> >> > >> > Also it depends what you are trying to do with async. Currently async >> > transport is only for sending messages to another node, we never think >> > of when we are the owning node. In this case the calling thread would >> > have to go down the interceptor stack and acquire any locks if it is >> > the owner, thus causing this "async" to block if you have any >> > contention on the given key. The use of another thread would allow >> > the calling thread to be able to return immediately no matter what >> > else is occurring. Also I don't see what is so wrong about having a >> > context switch to run something asynchronously, we shouldn't have a >> > context switch to block the user thread imo, which is very possible >> > with locking. >> >> This is an important notice! Locking would complicate the design a lot, >> because the thread in "async" mode should do only tryLocks - if this >> fails, further processing should be dispatched to another thread. Not >> sure if this could be implemented at all, because the thread may be >> blocked inside JGroups as well (async API is about receiving the >> response asynchronously, not about sending the message asynchronously). >> >> I don't say that the context switch is that bad. My concern is that you >> have a very limited amount of requests that can be processed in >> parallel. I consider a "request" something pretty lightweight in concept >> - but one thread per request makes this rather heavyweight stuff. >> >> We did talk in Farnborough/Palma about removing the current LockManager with >> a queue-based structure like the one used for ordering total-order >> transactions. And about removing the implicit stack in the current >> interceptor stack with an explicit stack, to allow resuming a command >> mid-execution. But the feeling I got was that neither is going to make it >> into 7.0. >> >> >> > >> >> +1 much cleaner, I love it. Actually wasn't aware the current code >> >> didn't do this :-( >> > This is what the current async transport does, but it does nothing with >> > Futures. >> >> Nevermind the futures, this is not the important part. It's not about >> async transport neither, it's about async executors. >> (okay, the thread was about dropping async transport, I have hijacked it) >> >> Radim >> >> -- >> Radim Vansa <rva...@redhat.com> >> JBoss DataGrid QA >> >> _______________________________________________ >> infinispan-dev mailing list >> infinispan-dev@lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/infinispan-dev >> >> _______________________________________________ >> infinispan-dev mailing list >> infinispan-dev@lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/infinispan-dev > > > -- > Galder Zamarreño > gal...@redhat.com > twitter.com/galderz > > Project Lead, Escalante > http://escalante.io > > Engineer, Infinispan > http://infinispan.org > > > _______________________________________________ > infinispan-dev mailing list > infinispan-dev@lists.jboss.org > https://lists.jboss.org/mailman/listinfo/infinispan-dev _______________________________________________ infinispan-dev mailing list infinispan-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/infinispan-dev
