The transaction you are referring to is a transaction on the KahaDB index and a new one will be created by KahaDB when calling that method so you don't need to worry about it. In terms of statefulness, you are correct that the order index tracks state of where it left off. But I believe it is safe to use the recover() method (which always resets the cursor and starts at the beginning) as there are things like duplicate detection in place so it should be able to handle it.
In fact, if you call browse() on a Topic from JMX it will eventually end up delegating to the recover method on the Topic Store and it will return up to the number of messages of the browse page size so it has been designed to be called multiple times because it will be called every time you call browse(). Here is how it is used and might be a good example for basing your code off of: https://github.com/apache/activemq/blob/activemq-5.14.2/activemq-broker/src/main/java/org/apache/activemq/broker/region/Topic.java#L638 For recoverNextMessages I don't remember if it would work or not without taking a closer look. Unfortunately I don't think there is really any other methods right now to try and iterate over the messages in the store. The best thing to do would be to write a quick test and see if it works for you. On Fri, Dec 16, 2016 at 3:26 PM, jahlborn <jahlb...@gmail.com> wrote: > So, digging into the message store recoverNextMessages() code, it's tough to > tell what is going in in terms of statefulness. That method certainly seems > like it would get me the information that i'm after. two concerns: 1. it > looks to be expecting an existing Transaction (maybe i already have one in > place since i'm working off of an existing session). 2. > "recoverNextMessages" seems to imply that it's basing the notion of "next" > off of current state and calling this method will change that state. do i > need to do something with the store state to ensure that i don't mess up > this state for normal message consumption? > > thanks for your help so far! > > > christopher.l.shannon wrote >> You should be able to implement your own MessageRecoveryListener and >> use the recover() or recoverNextMessages() methods on the MessageStore >> interface. The MessageStore object is part of the region Queue (it is >> inherited from the parent BaseDestination class) >> http://activemq.apache.org/maven/apidocs/org/apache/activemq/store/MessageStore.html >> >> Calling that method will iterate over each message in the store, load >> it into memory and then and pass it to the MessageRecoveryListener >> that you provide. If you are using KahaDB then calling these methods >> will lock the index and prevent other writes/reads from the store >> while executing the method. >> >> On Thu, Dec 15, 2016 at 11:09 AM, jahlborn < > >> jahlborn@ > >> > wrote: >>> We have activemq embedded in our product. Since it runs in the same jvm, >>> we >>> have various resource limits in place. These limits make the browsing >>> functionality somewhat less than ideal (you can only read so many >>> messages >>> in a large queue). I was wondering if someone who has deeper knowledge >>> of >>> activemq could suggest a way to read messages directly from the data >>> store >>> (or some other way to do unbounded browsing which doesn't use up all >>> system >>> memory). >>> >>> I already attempted this a bit myself by adding a method to the region >>> Queue >>> for first pulling from the "paged in" messages, and then directly from >>> the >>> "PendingMessageCursor messages" to read messages. However, despite the >>> fact >>> that the cursor is backed by the message store, it still seems to want to >>> "page in" messages, and also abides by the resource limits. (i was >>> borrowing code from Queue.getMessage(String id)). >>> >>> Is there any way to "bypass" the "paging in" logic and just read messages >>> directly from the message store? i'm okay with this being "slow", i'd >>> prefer to have a solution which works slowly rather than no solution at >>> all... >>> >>> >>> >>> -- >>> View this message in context: >>> http://activemq.2283324.n4.nabble.com/Custom-code-to-browse-messages-in-the-message-store-tp4720423.html >>> Sent from the ActiveMQ - User mailing list archive at Nabble.com. > > > > > > -- > View this message in context: > http://activemq.2283324.n4.nabble.com/Custom-code-to-browse-messages-in-the-message-store-tp4720423p4720542.html > Sent from the ActiveMQ - User mailing list archive at Nabble.com.
