[jboss-jira] [JBoss JIRA] (JGRP-1675) CreditRequest in FlowControl is not OOB

[Radim Vansa (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1675?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12796825#comment-12796825 ] 

Radim Vansa commented on JGRP-1675:
-----------------------------------

Seems that increasing the credit amount to high value is a workaround for the issue. The problem is that the load was really high in our test - like 15k messages per second - and if something (e.g. GC) breaks in, many messages are buffered in socket. When we start processing them again, we process some of them, sending the responses and decreasing the FC credits really fast. Then, the OOB tp is temporarily depleted (before we get the replenish) and the other messages get discarded - the fact is that the request is much smaller than the response, therefore the requestor can send many requests before reaching the FC credit limit but the amount of responses that can be sent is much lower.

This results in the sudden loss of many messages allowing situation described in comments above.
                
> CreditRequest in FlowControl is not OOB
> ---------------------------------------
>
>                 Key: JGRP-1675
>                 URL: https://issues.jboss.org/browse/JGRP-1675
>             Project: JGroups
>          Issue Type: Bug
>    Affects Versions: 3.4
>            Reporter: Radim Vansa
>            Assignee: Bela Ban
>             Fix For: 3.4
>
>
> I have recently observed a repeated situation where many (or all) threads have been stuck waiting for credits in FlowControl protocol.
> The credit request was not handled on the other node as this is non-oob message and some (actually many of them - cause unknown) messages before the request have been lost - therefore the request was waiting for them to be re-sent.
> However, these have not been re-sent properly as the retransmission request was not received - all OOB threads were stuck in the FlowControl protocol as these handled some other request and tried to send a response - but the response could not be sent until FlowControl gets the credits.
> The probability of such situation could be lowered by tagging the credit request to be OOB - then it would be handled immediately. If the credit replenish message would then be processed in regular OOB pool, this could get already depleted by many requests, but setting up the internal thread pool would solve the problem.
> Other consideration would be to allow releasing thread from FlowControl (let it send the message even without credits) if it waits there for too long.

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