[infinispan-dev] HotRod?? [ISPN-29 and a "custom protocol"]
Manik Surtani
manik at jboss.org
Mon Nov 30 07:26:16 EST 2009
On 29 Nov 2009, at 17:55, Alex Kluge wrote:
> HI,
>
>> I tend to like clearly defined requests and responses, so clients
>> can ask for information that they want. There are also events, so
>> that when something changes, the clients can receive asynchronous
>> events.
>
>> The problem with that approach is the way connections work.
>> Explicit > server -> client messages would require either open
>> client-side ServerSockets, or persistent connections which cannot
>> be guaranteed if there is a firewall separating things.
>
> In reading this you may notice that I favor use case driven design :)
>
> Yes, it is difficult to ensure that a client has accurate information,
> especially about the server topology. That is what drove me to the server
> side routing approach.
>
> For example. a client connects for the first time, how do they get the
> server topology? I would suggest either it be unneeded (the server does
> the routing), or the first thing they send is a request for it.
The servers *could* route if needed, client-side routing is purely an optimisation that clients may choose to implement.
> The same question applies to a client that has been disconnected for a
> period of time. The available solutions are a bit different here, because
> the client may have a server topology, but it may be out of date. So
> if we expect the client to be able to do the routing, it will have to
> provide a topology version to the server with the requests, and expect
> an update back when the version is out of date. Or, it could simply send
> a request for a topology update as the first request.
>
>> This is actually dealt-with. When a rebalance occurs,
>> requests sent to the "old" owner are proxied on to the new
>> one. Transparent to the caller.
>
> When could this stop? That is, when would you be guaranteed that all
> clients have an up to date topology? Or is this always available?
> If it is always available, how much value is provided by having the
> client determine the server to rout the request to?
It is always available. The value is that if the clients are able to handle routing, they reduce load on the server side. Now if this is a public setup with lots of different clients, you will always need server-side routing, but if you are running in a controlled environment and are able to guarantee that all clients will be able to route requests themselves, then you could optimise the backend for this (e.g., disable L1 caching).
> Does the client attempt to maintain connections to all the servers? Or
> does it open and close connections for each request?
Depends on how the client is designed. Possibly both approaches could be used, based on a configuration flag on the client. Depending on how large your server backend is (number of nodes), you would favour one option over the other.
>
>> persistent connections which cannot be guaranteed if there is a
>> firewall separating things.
>
> How prevalent is this case? I have used and seen a remote cache in several
> applications, and it has always been comparatively local to the
> application. If a reasonably long lived connection is not available, a
> lot of issues arise. Consider the use as an L2 cache, how can you
> guarantee the consistancy of the various L1 caches if they do not receive
> events from the L2 cache when data is written? Indeed, the protocol that I
> have is designed around the L2 cache usage scenario.
>
> I'll see what I can do about documenting it...
Yeah lets do that - I would recommend using the JBoss.org wiki pages so that the designs can be distilled by all of us and then linked to from the other Infinispan design pages.
Cheers
Manik
>
> Alex
>
>
>
>
>
> --- On Wed, 11/25/09, Manik Surtani <manik at jboss.org> wrote:
>
>> From: Manik Surtani <manik at jboss.org>
>> Subject: Re: [infinispan-dev] HotRod?? [ISPN-29 and a "custom protocol"]
>> To: "infinispan -Dev List" <infinispan-dev at lists.jboss.org>
>> Date: Wednesday, November 25, 2009, 5:01 AM
>>
>> On 24 Nov 2009, at 22:25, Alex Kluge wrote:
>>
>>> Hi,
>>>
>>> I've been a little busy recently tracking what
>> appears to be an issue
>>> with JBoss Cache under significant concurrent load,
>> but I have had some
>>> time to look at this.
>>>
>>>>> Are there requirements for an infinispan
>>>>> protocol documented anywhere?
>>>>
>>>> Manik and I discussed the extra bits that we think
>> the
>>>> binary protocol
>>>> should contain and these are now explained in:
>>>> http://www.jboss.org/community/wiki/HotRodProtocol
>>>
>>> I don see anything here that would be particularly
>> difficult.
>>> The only thing that confuses me is the exact meaning
>> of "piggy back".
>>> It sounds like "piggy back" as used here refers to
>> overloading a
>>> response and providing additional information in some
>> cases.
>>
>> That is precisely what it means. :-)
>>
>>> I tend
>>> to like clearly defined requests and responses, so
>> clients can ask
>>> for information that they want. There are also events,
>> so that when
>>> something changes, the clients can receive
>> asynchronous events.
>>
>> The problem with that approach is the way connections
>> work. Explicit server -> client messages would
>> require either open client-side ServerSockets, or persistent
>> connections which cannot be guaranteed if there is a
>> firewall separating things.
>>
>>> Perhaps if I had a slightly better understanding of
>> the desired
>>> behaviour I could fit the protocol to it.
>>
>> Sending additional information as a piggyback to usual
>> payload is a common technique, this is how HA EJB connectors
>> are commonly implemented in app servers. Essentially all
>> response streams a client may see would be in the following
>> format:
>>
>> [num-headers:
>> byte][headers][response-size: int][response: byte array]
>>
>> On the client, when parsing the stream, the response is
>> parsed and passed up to higher layers, along with a map of
>> headers which may contain additional info such as
>> server-side topology, which can be used to update the
>> client's list of targets and will affect client-side logic
>> when choosing where to send future requests.
>>
>>>
>>>>> - It is easier to coordinate the smaller
>> number of servers when a new
>>>>> one comes online, or goes
>> offline.
>>>
>>>> Hmmmm, I'm not sure I understand why this would be
>> a problem for client
>>>> side routing. The client's would get new cluster
>> formation information
>>>> next time they make a call. IOW, the response to
>> the client would
>>>> contain cluster formation info of the nodes
>> configured with hot rod
>>>> server, so no need to coordinate server
>> join/leaves with clients. This
>>>> is how clustered EJBs work in AS.
>>>
>>> Consider the case where you have a thousand clients,
>> and three servers.
>>> Each client sends a put or get request to the
>> appropriate server according
>>> to a consistent hash.
>>>
>>> Now, add a new server. If the clients are doing the
>> CH, then they all
>>> need to be consistent at the same time. Otherwise one
>> client may write
>>> data to one server, and another client may read or
>> write the same data
>>> to another server.
>>
>> This is actually dealt-with. When a rebalance occurs,
>> requests sent to the "old" owner are proxied on to the new
>> one. Transparent to the caller.
>>
>>> Consistency among a large number of clients becomes
>>> a hard problem. It is simply easier to manage the
>> dynamics when you
>>> have a simpler system under tighter control, such as a
>> set of servers.
>>
>> Right, and in such a case you may "dumb down" the
>> client. The way we see it, there are 3 degrees of
>> "intelligence" in clients, and this "degree of intelligence"
>> could be encoded (a single byte?) in the request when
>> talking to servers.
>>
>> 1. Dumb. Just spray requests to a load balancer which
>> uses a round-robin policy to talk to servers. Very
>> simple clients, only configured with a single endpoint which
>> is the LB. No extra information sent back to clients
>> from the servers.
>>
>> 2. Semi-smart: Clients have knowledge of server
>> topology, but clients do not engage in CH. No LB
>> needed, clients round-robin around the servers, potentially
>> use session affinity, clients resilient to connection
>> failure (can fail over). Servers need to send back
>> server topology whenever there are changes to the backend.
>>
>> 3. Smart: Clients have knowledge of server topology
>> as well as the CH function in effect. Clients can
>> direct requests to specific back-end nodes based on keys
>> involved, can load balance and fail over. Servers need
>> to send back server topology and hash codes of each server
>> node whenever there are changes to the backend.
>>
>> Good discussions anyway, lets keep these going...
>>
>> Cheers
>> Manik
>>
>>>
>>>
>>
>> Alex
>>>
>>>
>>>
>>> --- On Fri, 11/20/09, Galder Zamarreno <galder at redhat.com>
>> wrote:
>>>
>>>> From: Galder Zamarreno <galder at redhat.com>
>>>> Subject: Re: [infinispan-dev] ISPN-29 and a
>> "custom protocol"
>>>> To: infinispan-dev at lists.jboss.org
>>>> Date: Friday, November 20, 2009, 4:50 AM
>>>> Hi Alex,
>>>>
>>>> On 11/19/2009 06:02 PM, Alex Kluge wrote:
>>>>> Hi,
>>>>>
>>>>> > Is this protocol
>>>> documented somewhere?
>>>>>
>>>>> Putting this online is one of
>> the
>>>> main things I will be able to do
>>>>> along this path over the next
>> week.
>>>>>
>>>>> > Galder is working on
>> the
>>>> HotRod protocol which may well benefit
>>>>> > from this.
>>>>>
>>>>> Well, it may not be necessary to
>>>> reinvent it. We'll see. Are there
>>>>> requirements for an infinispan
>>>> protocol documented anywhere?
>>>>
>>>> Manik and I discussed the extra bits that we think
>> the
>>>> binary protocol
>>>> should contain and these are now explained in:
>>>> http://www.jboss.org/community/wiki/HotRodProtocol
>>>>
>>>> If you can add docu of your binary protocol there,
>> we can
>>>> look into
>>>> accomodation this stuff into your binary protocol
>>>> potentially?
>>>>
>>>>>
>>>>> > The plan is for HotRod
>> to
>>>> support (but not mandate)
>>>>> > client-side CH
>>>>>
>>>>> I did this originally, however,
>> I
>>>> moved to a server side message
>>>>> routing for a few reasons.
>>>>>
>>>>> - It is easier to coordinate the
>>>> smaller number of servers when a new
>>>>> one comes online, or goes
>>>> offline.
>>>>
>>>> Hmmmm, I'm not sure I understand why this would be
>> a
>>>> problem for client
>>>> side routing. The client's would get new cluster
>> formation
>>>> information
>>>> next time they make a call. IOW, the response to
>> the client
>>>> would
>>>> contain cluster formation info of the nodes
>> configured with
>>>> hot rod
>>>> server, so no need to coordinate server
>> join/leaves with
>>>> clients. This
>>>> is how clustered EJBs work in AS.
>>>>
>>>>>
>>>>> - It allows fewer connections
>> per
>>>> server, client side routing requires
>>>>> that each client connect
>> to
>>>> each server. For our scale, thousands of
>>>>> servers, this is an
>> issue.
>>>>
>>>> That's a good point.
>>>>
>>>>>
>>>>> - It guarantees a consistent
>> mapping
>>>> of data to servers for potentially
>>>>> disperate clients.
>>>>>
>>>>> - It makes the client side code
>>>> easier to write.
>>>>
>>>> True :)
>>>>
>>>>>
>>>>>
>>>>> That said, if the client does do
>> the
>>>> hashing, the server will still
>>>>> do it, and make sure that the
>> data
>>>> arrives at the correct server. So
>>>>> nothing prevents the client from
>>>> doing the hashing.
>>>>>
>>>>>
>>
>>>>
>>
>>>>
>> Alex
>>>>>
>>>>>
>>>>> --- On Mon, 11/16/09, Manik Surtani<manik at jboss.org>
>>
>>>> wrote:
>>>>>
>>>>>> From: Manik Surtani<manik at jboss.org>
>>>>>> Subject: Re: [infinispan-dev] ISPN-29 and
>> a
>>>> "custom protocol"
>>>>>> To: "infinispan -Dev List"<infinispan-dev at lists.jboss.org>
>>>>>> Date: Monday, November 16, 2009, 5:06 AM
>>>>>> Hi Alex - comments in line:
>>>>>>
>>>>>> On 16 Nov 2009, at 07:25, Alex Kluge
>> wrote:
>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> It is worth
>> mentioning that I
>>>> have a full
>>>>>> implementation of a
>>>>>>> client-server binary protocol used
>> for
>>>> jboss-cache,
>>>>>> which is similar
>>>>>>> to the current project and can be
>> easily
>>>> adapted to
>>>>>> it. There are a
>>>>>>> number of interesting points
>>>>>>>
>>>>>>> - Built on Apache
>> MINA
>>>> framework, but
>>>>>> the layers are well separated,
>>>>>>> so
>> replacing
>>>> one would not be
>>>>>> too difficult.
>>>>>>
>>>>>> Nice.
>>>>>>
>>>>>>> - Language
>> neutral
>>>> binary protocol
>>>>>> (non Java clients are planned).
>>>>>>
>>>>>> Is this protocol documented somewhere?
>>>> Galder is
>>>>>> working on the HotRod protocol which may
>> well
>>>> benefit from
>>>>>> this.
>>>>>>
>>>>>>> - Integrated into
>>>> Jboss Cache as an
>>>>>> L2 cache, but easily used
>>>>>>>
>> independently.
>>>>>>> - Performance is
>> quite
>>>> reasonable,
>>>>>> with request/response cycles on
>>>>>>> the order
>> of
>>>> 600 microseconds
>>>>>> for small request/response.
>>>>>>> - Easily
>> extensible, a
>>>> different
>>>>>> codec can be supplied to support
>>>>>>> different
>>>> protocols. Some
>>>>>> refactoring could be done to make this
>>>>>>> much
>> easier.
>>>>>>> - Non trivially
>> tested
>>>> already.
>>>>>>> - Inherently
>>>> asynchronous -
>>>>>> synchronous responses are achieved by
>>>>>>>
>> immediately
>>>> waiting on the
>>>>>> response future object.
>>>>>>> - Server side
>>>> consistent hashing,
>>>>>> clients connect to any server.
>>>>>>
>>>>>> The plan is for HotRod to support (but
>> not
>>>> mandate)
>>>>>> client-side CH as well for "smart"
>> connections.
>>>>>>
>>>>>>> There is raw source at
>>>>>>> http://www.vizitsolutions.com/org.jboss.cache.tcpcache.tar.gz
>>>>>>>
>>>>>>> I'll see about some explanations and
>> examples
>>>> over the
>>>>>> next weeks.
>>>>>>
>>>>>> Great!
>>>>>>
>>>>>>> This was intended to be contributed
>> back to
>>>> the Jboss
>>>>>> Cache project from the beginning, hence
>> the
>>>> organization
>>>>>> into jboss.cache packages. Oh, and
>>>>>>> I never gave it a snazzy name - I just
>> called
>>>> it the
>>>>>> Jboss Cache binary
>>>>>>> protocol.
>>>>>>
>>>>>> :)
>>>>>>
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> Alex
>>>>>>>
>>>>>>> --- On Wed, 8/19/09, Manik
>> Surtani<manik at jboss.org>
>>>>>> wrote:
>>>>>>>
>>>>>>>> From: Manik Surtani<manik at jboss.org>
>>>>>>>> Subject: Re: [infinispan-dev]
>> ISPN-29 and
>>>> a
>>>>>> "custom protocol"
>>>>>>>> To: "Jeff Ramsdale"<jeff.ramsdale at gmail.com>
>>>>>>>> Cc: infinispan-dev at lists.jboss.org
>>>>>>>> Date: Wednesday, August 19, 2009,
>> 12:05
>>>> PM
>>>>>>>> Nice one Jeff ... so far this is
>>>>>>>> winning in my mind!
>>>>>>>>
>>>>>>>> On 19 Aug 2009, at 18:01, Jeff
>> Ramsdale
>>>>>>>> wrote:
>>>>>>>> How about Hot Rod? It has a
>> connection to
>>>> the
>>>>>>>> word "custom" and implies
>> speed...
>>>>>>>> -jeff
>>>>>>>>
>>>>>>>> On Wed, Aug 19, 2009 at 7:05 AM,
>>>>>>>> Manik Surtani<manik at jboss.org>
>>>>>>>> wrote:
>>>>>>>> Regarding
>>>>>>>> ISPN-29 [1], I've made some notes
>> about
>>>> what this
>>>>>> will
>>>>>>>> provide on this wiki page
>> [2]. I'm
>>>> kinda
>>>>>> tired
>>>>>>>> of referring to the
>>>>>>>> 'custom binary protocol' as a
>> 'custom
>>>> binary
>>>>>>>> protocol'! Can anyone
>>>>>>>> think of a snazzy name for this
>> protocol?
>>>>>> Keep in
>>>>>>>> mind that we would
>>>>>>>> want others to implement clients
>> using
>>>> this
>>>>>> protocol as
>>>>>>>> well on other
>>>>>>>> platforms.
>>>>>>>>
>>>>>>>> Here are a few thoughts to get
>> the
>>>> creative
>>>>>> juices
>>>>>>>> flowing:
>>>>>>>>
>>>>>>>>
>> * ICBP
>>>> (Infinispan
>>>>>> cache binary
>>>>>>>> protocol - BORING!)
>>>>>>>>
>> *
>>>> Adhesive (the 'glue'
>>>>>>>> between the client and server)
>>>>>>>>
>> *
>>>> Elastiglue
>>>>>>>>
>> *
>>>> StickyFingers (after
>>>>>> the
>>>>>>>> Rolling Stones album?)
>>>>>>>>
>>>>>>>> - Manik
>>>>>>>>
>>>>>>>> [1] https://jira.jboss.org/jira/browse/ISPN-29
>>>>>>>> [2] http://www.jboss.org/community/wiki/Clientandservermodules
>>>>>>>> --
>>>>>>>> Manik Surtani
>>>>>>>> manik at jboss.org
>>>>>>>> Lead, Infinispan
>>>>>>>> Lead, JBoss Cache
>>>>>>>> http://www.infinispan.org
>>>>>>>> http://www.jbosscache.org
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>> _______________________________________________
>>>>>>>> infinispan-dev mailing list
>>>>>>>> infinispan-dev at lists.jboss.org
>>>>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>>>>>
>>>>>>>>
>>>>>>>> --Manik
>>>>>>>> Surtanimanik at jboss.orgLead,
>>>>>>>> InfinispanLead, JBoss Cachehttp://www.infinispan.orghttp://www.jbosscache.org
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> -----Inline Attachment
>> Follows-----
>>>>>>>>
>>>>>>>>
>>>> _______________________________________________
>>>>>>>> infinispan-dev mailing list
>>>>>>>> infinispan-dev at lists.jboss.org
>>>>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>> _______________________________________________
>>>>>>> infinispan-dev mailing list
>>>>>>> infinispan-dev at lists.jboss.org
>>>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>>>
>>>>>> --
>>>>>> Manik Surtani
>>>>>> manik at jboss.org
>>>>>> Lead, Infinispan
>>>>>> Lead, JBoss Cache
>>>>>> http://www.infinispan.org
>>>>>> http://www.jbosscache.org
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>> _______________________________________________
>>>>>> infinispan-dev mailing list
>>>>>> infinispan-dev at lists.jboss.org
>>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>> _______________________________________________
>>>>> infinispan-dev mailing list
>>>>> infinispan-dev at lists.jboss.org
>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>
>>>> --
>>>> Galder Zamarreño
>>>> Sr. Software Engineer
>>>> Infinispan, JBoss Cache
>>>> _______________________________________________
>>>> infinispan-dev mailing list
>>>> infinispan-dev at lists.jboss.org
>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> infinispan-dev mailing list
>>> infinispan-dev at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>
>> --
>> Manik Surtani
>> manik at jboss.org
>> Lead, Infinispan
>> Lead, JBoss Cache
>> http://www.infinispan.org
>> http://www.jbosscache.org
>>
>>
>>
>>
>>
>> _______________________________________________
>> infinispan-dev mailing list
>> infinispan-dev at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>
>
>
>
>
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--
Manik Surtani
manik at jboss.org
Lead, Infinispan
Lead, JBoss Cache
http://www.infinispan.org
http://www.jbosscache.org
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