Agreed that async performs better than sync in general but the catch here to me is the "order".
The whole point of async is to do out of order processing by which I mean say if a request 1 comes in at time t1 and a request 2 comes in at time t2 where t1 < t2 and say now that t1 is taking longer to process than t2 in which case request 2 should get a response first and subsequently a response for request 1. This is where I would imagine all the benefits of async come in but the moment you introduce order by saying for Last Write Wins all the async requests should be processed in order I would imagine all the benefits of async are lost. Let's see if anyone can comment about how it works inside C*. Thanks! On Mon, Feb 20, 2017 at 10:54 PM, Dor Laor <d...@scylladb.com> wrote: > Could be. Let's stay tuned to see if someone else pick it up. > Anyway, if it's synchronous, you'll have a large penalty for latency. > > On Mon, Feb 20, 2017 at 10:11 PM, Kant Kodali <k...@peernova.com> wrote: > >> Thanks again for the response! if they mean it between client and server >> I am not sure why they would use the word "replication" in the statement >> below since there is no replication between client and server( coordinator). >> >> "Choose between synchronous or asynchronous replication for each update." >>> >> >> Sent from my iPhone >> >> On Feb 20, 2017, at 5:30 PM, Dor Laor <d...@scylladb.com> wrote: >> >> I think they mean the client to server and not among the servers >> >> On Mon, Feb 20, 2017 at 5:28 PM, Kant Kodali <k...@peernova.com> wrote: >> >>> Also here is a statement from C* website >>> >>> "Choose between synchronous or asynchronous replication for each update. >>> " >>> >>> http://cassandra.apache.org/ >>> >>> Looks like we can choose then either sync or async then? >>> >>> On Mon, Feb 20, 2017 at 5:25 PM, Kant Kodali <k...@peernova.com> wrote: >>> >>>> Hi Dor, >>>> >>>> Great response! My comments are inline. >>>> >>>> Thanks a lot, >>>> kant >>>> >>>> >>>> On Mon, Feb 20, 2017 at 4:41 PM, Dor Laor <d...@scylladb.com> wrote: >>>> >>>>> I sent this answer but it bounced off the user@apache. >>>>> Here is the email anyway: >>>>> >>>>> ---------- Forwarded message ---------- >>>>> From: Dor Laor <d...@scylladb.com> >>>>> Date: Mon, Feb 20, 2017 at 4:37 PM >>>>> Subject: Re: Does C* coordinator writes to replicas in same order or >>>>> different order? >>>>> To: d...@cassandra.apache.org >>>>> Cc: user@cassandra.apache.org >>>>> >>>>> >>>>> + The C* coordinator send async write requests to the replicas. >>>>> This is very important since it allows it to return a low latency >>>>> reply to the client once the CL is reached. You wouldn't want >>>>> to serialize the replicas one after the other. >>>>> >>>> >>>> *so coordinator wont wait until a CL is reached before it >>>> process another request? * >>>> >>>>> >>>>> + The client <-> server sync/async isn't related to the coordinator >>>>> in this case. >>>>> >>>>> + In the case of concurrent writes (always the case...), the time >>>>> stamp >>>>> sets the order. Note that it's possible to work with client >>>>> timestamps or >>>>> server timestamps. The client ones are usually the best choice. >>>>> >>>> >>>> *In theory, Why we say concurrent writes they should have the same >>>> timestamp right? What I am really looking for is that if I send write >>>> request concurrently for record 1 and record 2 are they guaranteed to be >>>> inserted in the same order across replicas? (Whatever order coordinator may >>>> choose is fine but I want the same order across all replicas and with async >>>> replication I am not sure how that is possible ? for example, if a request >>>> arrives with timestamp t1 and another request arrives with a timestamp t2 >>>> where t1 < t2...with async replication what if one replica chooses to >>>> execute t2 first and then t1 simply because t1 is slow while another >>>> replica choose to execute t1 first and then t2..how would that work? )* >>>> >>>>> >>>>> Note that C* each node can be a coordinator (one per request) and its >>>>> the desired case in order to load balance the incoming requests. Once >>>>> again, >>>>> timestamps determine the order among the requests. >>>>> >>>>> Cheers, >>>>> Dor >>>>> >>>>> On Mon, Feb 20, 2017 at 4:12 PM, Kant Kodali <k...@peernova.com> >>>>> wrote: >>>>> >>>>>> Hi, >>>>>> >>>>>> when C* coordinator writes to replicas does it write it in same order >>>>>> or >>>>>> different order? other words, Does the replication happen >>>>>> synchronously or >>>>>> asynchrnoulsy ? Also does this depend sync or async client? What >>>>>> happens in >>>>>> the case of concurrent writes to a coordinator ? >>>>>> >>>>>> Thanks, >>>>>> kant >>>>>> >>>>> >>>>> >>>>> >>>> >>> >> >
