[jboss-jira] [JBoss JIRA] (JGRP-1564) TP: handling of message batches

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1564?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12749195#comment-12749195 ] 

Bela Ban commented on JGRP-1564:
--------------------------------

Hmm, delivering a message batch one-by-one (each message as a separate task in the thread pool) slows things down: as tasks get added to the queue when all core threads have been started, each task Tn gets executed after the preceding task Tn-1. This results in an increasingly longer executions time for queued tasks, as each task has to wait until all tasks in the queue ahead of it have been processed.

This 'queueing effect' didn't come into play much before as a message batch of N messages was executed by *1* thread, not by *N* threads !

At this point, we could look into writing our own thread pool (which for example goes from min to max threads *before* queueing messages), or take another look at MSG_BATCH. I'll do the latter first. The promising thing about it is that we'd go back to the previous behavior of only using 1 thread to handle 1 message batch, which is fast.
                
> TP: handling of message batches
> -------------------------------
>
>                 Key: JGRP-1564
>                 URL: https://issues.jboss.org/browse/JGRP-1564
>             Project: JGroups
>          Issue Type: Enhancement
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 3.3
>
>
> When B receives a batch of 5 messages from A (unicast or multicast), then B uses the *same thread* to send the 5 messages up (this isn't the case for OOB messages).
> It would be more efficient to either have different threads passing the 5 messages up, or use a new *message batch event type* to pass all 5 messages up in one go.
> The advantage of different threads is that all 5 threads add their message to the window, but only 1 removes them and passes them up, rather than each thread adding and removing its own message (fewer lock acquisitions).
> We could try moving the unmarshalling of messages and message batches into TP.receive(). If a batch was received, that code could unmarshal the 5 messages and pass them to corresponding thread pools to send them up.
> The unmarshalling shouldn't take long, so TP.receive() should return quickly.
> This approach would allow us to send OOB messages in message batches, too (currently not allowed).
> The advantage of a message batch is that we pass *one* event up the stack, passing only *once* through all protocols from TP to UNICAST/2 and NAKACK/2, and not 5 times. Also, adding 5 messages to the window under the same lock is more eficient than acquiring the lock 5 times. Ditto for removal.
> The disadvantage is that we now need to handle a different event type (all protocols under UNICAST/NAKACK), e.g. ENCRYPT, SIZE, FRAG(2) (if placed under UNICAST/NAKACK), COMPRESS etc.
> Also, this solution is not symmetric, ie. messages are batched at the transport level, and should be unbatched at the transport level of the receiver(s) as well...

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