Here is my use case: I am developing a trading application and i want to send incremental stock updates (bidQty etc) to active consumers instead of the whole quote and a snapshot update to a new consumer (to start with).
Now, is it possible to override any ActiveMQ's class (implementors of Topic) to achieve this behavior? Any clues on this would be helpful .
If the same is possible in any other openSource provider, please let me know.
This is NOT a case where you simply can change the implementation of topic. You should actually avoid changing the implementation of core ActiveMQ features to solve specific business requirements. Fixing bugs and adding core messaging features is another thing.
There are multiple ways to solve your use case with regular ActiveMQ features.
Separate Sync and Update channel
I would probably divide the "sync/snapshot" channel from the "incremental update" channel.
One way is to implement the "snapshot-sync" as JMS request/reply where the consumer asks the provider for a sync, then continues to rely on incremental updates pushed via the topic.
Advisory messages and Selectors
You can also implement it all using a single topic using a mix of AdvisoryMessages and JMS Selectors.
An idea (you can do this in many ways):
Introduce two message properties: MsgType and Receiver
Mark each incremental update with MsgType=inc
Mark each snapshot with some client id of the consumer, Receiver=.
Have the producer listen to advisory messages from ActiveMQ and and fire a snapshot/sync message marked with Receiver= and MsgType=snapshot when there is a new client subscribing the stock topic.
The client subscribes with a selector of something like
MsgType='inc' OR (MsgType='snapshot' AND Receiver=<me>)
This way you can trigger snapshot syncs with specific clients as well as incremental updates for all clients.
If you start think about the dynamics you already have, you can probably think of another ten or so solutions.
Retroactive Consumers
You might have some use of a Retroactive Consumer - the example actually shows a scenario similar to yours.
Related
We have a requirement to copy messages from one ActiveMQ broker to another. Here the message has to just copy and the message should exist in both broker.
I can think of a custom application that subscribes to a certain destination and read that message and re-post the messages to the destination in multiple brokers.
I do not have access to make changes in the Broker so I couldn't think of Network of Brokers option.
Is there any best practice or tools available to copy A-MQ messages from one broker to another?
Without having access to the target broker, as far as I know and I have read, I believe there is not shortcut to avoid the custom application that re-post those messages.
However, depending on the messages you want to re-post, there might be some functionalities offered by ActiveMQ that could facilitate your implementation (but they would not be for free, regarding the computational costs).
For example, in the case you want to copy ALL the messages sent through that broker to the other, then you might consider using Mirrored Queues, with a specific prefix (e.g. "copy"), that would allow you to just have a single consumer using a wildcard after that prefix (e.g. "copy.>"). That consumer would get ALL the messages sent to the broker, and it would simplify your implementation since you would just have to care about that single consumer and re-post from it. However this has costs, since as it is described in the documentation, enabling the mirrored queues will make a duplicate of each queue/topic in the system, and will post each message twice. You need to consider if this is an important inconvenient in your case, depending on the amount of messages and the available memory that your broker disposes.
In case you just wanted to copy SOME of the messages and not all, then I believe the most elegant way to handle it is by creating an abstraction of your Consumer class (or specific implementation), and use that special implementation for those queues you want to re-post. That class would be responsible of re-posting the messages to the other broker, in a way that would be transparent from the other Consumer class when using it.
I have talked above about consumers, but the same concept could apply to topics and subscribers. Hope these ideas help :)
I'm confused when it comes to JMS Queue/Topic. What I want is messages should go to every subscriber and I want subscribers to receive messages from inactive time when they become active. However, I don't have control over whether or not subscribers have durable subscription. Is there a way to set up a persistent Queue, and set it up so that every subscriber will receive same message? And how to set this up using spring config
Thanks much.
This is mostly a question where the design of your system affects the outcome.
You could use UI tooling to create durable subscriptions for the clients that need to but that is cumbersome and error prone. You could use something like camel or other configuration on the target broker to fanout messages from an incoming Queue to outgoing Queues that map to the consumer subscriptions.
It all depends mostly on the requirements and your overall design so a real answer is beyond the scope of a SO answer without you doing some more legwork to narrow the scope a bit. JMS itself does not define any answer for this so it will come down a bit to the broker you've chosen and possibly other third party tooling that you might pick to do what you need.
I'm looking at swapping out ActiveMQ with RabbitMQ for a few reasons. I currently have multiple services which are each capable of publishing events (and they publish those events to a specific VirtualTopic in AMQ). Each of the services is also capable of consuming messages from the other services. Consumers are set up such that they subscribe as a consumer to a queue on the VirtualTopic.
This buys me the ability to fan messages out to multiple queues (topic-like functionality) while keeping the benefits of queues (load balancing and persistence).
It seems like this is roughly equivalent to RabbitMQ's fanout exchange. However, the part that I found very useful in ActiveMQ is that the producer doesn't need to have any knowledge of the consumers. It simply publishes to the virtual topic. It seems that in RabbitMQ, when the exchange is created, I need a definitive of queues to publish that message to.
tl;dr
Is there any routing scheme in RabbitMQ that is equivalent to ActiveMQ's Virtual Topic, such that I can produce messages to a topic that are distributed to any queue that has been created off of that Virtual Topic, without requiring a hard-coded routing scheme somewhere in RMQ?
I realized after posting this question that it is pretty trivial to do this (not sure why I never thought of it before).
I was looking at it from the wrong direction, wondering how I could automatically have the publisher configure queues for the recipients - which isn't the right way to approach this question.
Instead, I have the subscribers, when they start up, bind themselves to the exchange that the publisher users, which provides in the inversion of control I'm looking for (publishers need not know anything about their consumers).
I need some help with topics and selectors.
I have a scenario with a topic having multiple durable subscribers (each with a selector)
not all messages going into the topic aren't read by the consumers - because of unmatching selectors.
This is correct behavior.
However the problem occurs when the unmatched messages reach a certain quantity threshold, because at that point no other messages are being delivered to the consumers
activemq tries to dispatch those old unmatchable messages, but since there is no consumer for them everything is stuck
can anybody help with this?
My setup is ActiveMq 5.5
is there some configuration option, or is it just a flawed design?
I'd say this is a flawed design given there are better alternatives and perhaps a bug in ActiveMQ.
First question: is your producer publishing to this topic setting the JMSExpiration header on those messages?
If yes, the first thing I'd do is create a Jira issue detailing the scenario you described above, because it does seem incorrect that ActiveMQ will continue hold on to and continue send messages for which no selectors apply.
As for flawed design, the minute you hear yourself saying "I need durable subscribers" and you are using ActiveMQ, you should immediately turn to using Virtual Destinations instead. Virtual Destinations have the advantages of topics in that a producer can send a message to a destination and have that message propagated to N number of other destinations for consumption, but doesn't have the disadvantages that come with having durable subscribers on a topic. Read more about Virtual Destinations here.
This is related to the way that ActiveMQ handles sparse selectors. The current implementation doesn't page into the store to look for message matching sparse selectors so you need to make some configuration changes to try and work around this. You can set the maxBrowsePageSize in the configured destination policy, the default is 400. See this page.
Virtual destinations in ActiveMQ is probably the better choice, it almost always is when thinking about using durable subscribers. You could however add some message expiration to you messages and configure the policy to expire messages on inactive durable subscribers if you use a SNAPSHOT version of ActiveMQ 5.6.
It does seem like a bug, (or dashedly inconvenient at the least) but there is a work around using Virtual Destinations.
Quote:
Note that making a topic virtual does add a small CPU overhead when
sending messages to the topic but it is fairly small. From version
5.4, dispatch from virtual topics to subscription queues can be
selectorAware such that only messages that match one of the existing
subscribers are actually dispatched. Using this option prevents the
build up of unmatched messages when selectors are used by exclusive
consumers.
Is is there some way to put a publish between clients in the network in Progress 4GL.
An (ugly) way would be to "publish" (write) to the db and let all clients poll the db - but of course I would like to avoid that.
I am using in Progress OpenEdge Release 10.0B02.
No. There is no way to use the built-in PUBLISH and SUBSCRIBE statements across a session boundary.
Its one of those things that people ask product management for from time to time but it never seems to make it onto the planned feature list.
You may be able to use a JMS like Apache ActiveMQ for your purposes. The publisher would be known as a producer, and the subscriber would be known as a consumer. ActiveMQ supports the STOMP protocol; there is an open source OpenEdge ABL framework I wrote that will allow you to create a producer or consumer in pure ABL using STOMP frames.