[jboss-jira] [JBoss JIRA] (JGRP-2171) New bundler with max_bundle_size for each destination

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-2171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13418649#comment-13418649 ] 

Bela Ban edited comment on JGRP-2171 at 6/9/17 2:49 AM:
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The current impl of {{TransferQueueBundler}} calls {{take()}} on the main-queue, then {{drainTo()}}. This acquires the lock on the main-queue twice, which is bad as sender threads also acquire the same lock to add their messages to the main queue.

Since there is no blocking {{drainTo()}}, let's implement this in {{RingBuffer}} and use {{RingBuffer}} instead of {{ArrayBlockingQueue}} for the main-queue. Having the bundler thread lock the main-queue once instead of twice should result in less contention on the main-queue, and perhaps slightly better perf, and it would also simplify the code.

Perhaps the simplification is the more important aspect, as {{take()}} is only called when the inner loop calling {{drainTo()}} terminated, no more message were in the main-queue. This should not happen often when many message are sent.



was (Author: belaban):
The current impl of {{TransferQueueBundler}} calls {{take()}} on the main-queue, then {{drainTo()}}. This acquires the lock on the main-queue twice, which is bad as sender threads also acquire the same lock to add their messages to the main queue.

Since there is no blocking {{drainTo()}}, let's implement this in {{RingBuffer}} and use {{RingBuffer}} instead of {{ArrayBlockingQueue}} for the main-queue. Having the bundler thread lock the main-queue once instead of twice should result in less contention on the main-queue, and perhaps slightly better perf.

> New bundler with max_bundle_size for each destination
> -----------------------------------------------------
>
>                 Key: JGRP-2171
>                 URL: https://issues.jboss.org/browse/JGRP-2171
>             Project: JGroups
>          Issue Type: Feature Request
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 4.0.4
>
>
> The current bundlers queue all messages and when the total size of all messages for all destinations would exceed {{max_bundle_size}}, message batches for each destination are sent.
> This negatively affects latency-sensitive applications, e.g. when we have a queue such as this: {{A B B C B B D B B}}, then the message for A has to wait until either the queue is full ({{max_bundle_size exceeded}}), or no more messages are received (and then we send the batches anyway).
> The goal is to write a new bundler which keeps a count for _each destination_ and sends batches to different destinations sooner. Also introduce a counter {{num_flips}} (find a better name!), which determines when a message batch is to be sent.
> This counter is decremented when a message to be sent has a destination that's different from the previous destination. When the counter is 0, we send the batch to the previous destination(s).
> We have a main queue, into which the senders write, and a runner thread (same as {{run()}} in TransferQueueBundler), which continually removes messages from the main queue and inserts them into queues for each destination.
> So 1 main queue and 1 queue for each destination.
> h4. Example:
> * {{num_flips}} is 2
> * A message for A is sent, added to the main queue and removed by the runner. It is queued in A's queue
> * Another message for A is sent. Also queued (A's queue: {{A A}})
> * A message to B is sent: A's {{num_flips}} is now 1. A's queue is {{A A}}, B's queue is {{B}}
> * Another message to A is sent. This resets A's {{num_flips}} to 2, B's {{num_flips}} is now 1
> * 2 messages to C are sent. This causes {{num_flips}} for A and B to be 0, so the batches to A (with 3 msgs) and B (1 msg) are also sent
> * No more messages are received, so the batch to C is also sent
> The value of {{num_flips}} should be computed as the rolling (weighted) average of the number of *adjacent messages to the same destination*. It is maintained for each destination separately (probably in the queue for that destination).
> h4. Misc
> * Should the sending of batches be delegated to a thread pool?
> * Should the senders add their messages directly to the destination queues instead of the main queue? That would result in less contention on the main queue, but it would also require 1 thread per destination queue, which creates too many threads...



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