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From Gary Tully <gary.tu...@gmail.com>
Subject Re: Producer Flow Control - what is AUTHORITATIVE?
Date Fri, 05 Nov 2010 18:19:42 GMT
there should be a message logged, at info level I think, at least on
trunk I see it.

On 5 November 2010 18:13, dcheckoway <dcheckoway@gmail.com> wrote:
>
> Thanks Gary.  I think we switched to vmQueueCursor at one point several
> weeks ago as an attempt to get better throughput...it was a desperate
> attempt that ended up working (made things faster), and so we kept
> vmQueueCursor enabled.  I now understand that memory is the limiting factor
> in this config.
>
> That being said, it might be helpful if activemq logged a warning about
> this.  i.e. "You turned producerFlowControl off but we're overriding your
> setting in order not to blow up....and here's why..."  At least something in
> activemq log output would be extremely helpful in identifying the fact that
> my setting was overridden.  Anyway, just a suggestion.
>
> Thanks again for the reply!
>
> Dan
>
>
> On Fri, Nov 5, 2010 at 1:59 PM, Gary Tully [via ActiveMQ] <
> ml-node+3029106-1912193586-140184@n4.nabble.com<ml-node%2B3029106-1912193586-140184@n4.nabble.com>
>> wrote:
>
>> The default behavior for the broker is to block a send pending
>> resources b/c exceeding resource limits could blow the VM with OOM,
>> producer flow control is about blocking producers before the client
>> does a send, rather than blocking on the broker, b/c blocking on the
>> broker will block the connection, not just the producer.
>>
>> So you have a memory limit, a vm message cursor, which will hold all
>> messages in memory and you have disabled producer flow control... so
>> when the memory limit is reached as the queue depth increased, the
>> send blocks on the broker till some memory is released by a consumer
>> taking some messages. So you see a stop start effect on your producer.
>>
>> The problem is the vmQueueCursor, this keeps all messages in memory
>> and will consume all of your destination memory limit.
>>
>> If you revert to the default store cursor <storeCursor/>, it will
>> cache messages in memory up to some portion of the queue limit and
>> leave the rest in the store.
>> So when you have fast consumers they can be served from the cache and
>> when you have slow consumers and exceed the cache, the messages will
>> get paged in from the store on demand.
>>
>> More detail on cursors at http://activemq.apache.org/message-cursors.html
>>
>>
>> On 5 November 2010 17:30, dcheckoway <[hidden email]<http://user/SendEmail.jtp?type=node&node=3029106&i=0>>
>> wrote:
>>
>> >
>> > 5.3.2, 5.4.1, and 5.5-SNAPSHOT -- doesn't matter which version, but I'm
>> > currently running 5.5-SNAPSHOT.  It's running with the stock persistence
>> > enabled and the stock -Xmx memory settings.
>> >
>> > PROBLEM: as consumers slow down, producers slow down -- despite
>> > producerFlowControl explicitly being disabled.
>> >
>> > I'm having trouble understanding what AUTHORITATIVELY enables/disables
>> > producer flow control.  This page
>> > (http://activemq.apache.org/producer-flow-control.html) talks about
>> > conditions that would cause flow control to happen.  It's extremely vague
>>
>> > about memoryLimit, systemUsage, etc., but it implies that those are
>> factored
>> > in.  But it also says you can disable flow control...which I have done.
>> > What's authoritative?  Why is ActiveMQ doing flow control when I asked it
>>
>> > not to?
>> >
>> > Here's a snippet from my activemq.xml:
>> >
>> >                <policyEntry queue=">" producerFlowControl="false"
>> > memoryLimit="20mb">
>> >                  <pendingQueuePolicy>
>> >                    <vmQueueCursor/>
>> >                  </pendingQueuePolicy>
>> >                </policyEntry>
>> >
>> > I'm doing sync sends to my queue (at least I believe I am, by virtue of
>> NOT
>> > doing explicitly async sends).  As consumers slow down, the producers get
>>
>> > blocked.  Can somebody please tell me why producer flow control is still
>> > kicking in?  If the policyEntry->producerFlowControl setting is not
>> > AUTHORITATIVE, maybe somebody can tell me what is?
>> >
>> > Is the vmQueueCursor conflicting with producerFlowControl="false" in some
>>
>> > way?
>> >
>> > Are the default systemUsage/memoryLimit settings conflicting or causing
>> > producer flow control to kick in?  Is the memoryLimit="20mb" on my queue
>> > conflicting?
>> >
>> > The biggest piece that I don't understand is: (a) IF a queue grows in
>> size
>> > beyond some limit (which is very hazy to me) it allows producer flow
>> control
>> > to kick in, and (b) if that's the case, how is that limit derived?  The
>> > combination of systemUsage/memoryLimit settings have always been
>> extremely
>> > elusive to me.
>> >
>> > I really need help understanding how I can, WITHOUT QUESTION, turn
>> producer
>> > flow control OFF COMPLETELY.
>> >
>> > Thanks!
>> >
>> > -----
>> > Dan Checkoway
>> > dcheckoway gmail com
>> > --
>> > View this message in context:
>> http://activemq.2283324.n4.nabble.com/Producer-Flow-Control-what-is-AUTHORITATIVE-tp3029064p3029064.html<http://activemq.2283324.n4.nabble.com/Producer-Flow-Control-what-is-AUTHORITATIVE-tp3029064p3029064.html?by-user=t>
>> > Sent from the ActiveMQ - User mailing list archive at Nabble.com.
>> >
>>
>>
>>
>> --
>> http://blog.garytully.com <http://blog.garytully.com?by-user=t>
>> http://fusesource.com <http://fusesource.com?by-user=t>
>>
>>
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>
>
> -----
> Dan Checkoway
> dcheckoway gmail com
> --
> View this message in context: http://activemq.2283324.n4.nabble.com/Producer-Flow-Control-what-is-AUTHORITATIVE-tp3029064p3029126.html
> Sent from the ActiveMQ - User mailing list archive at Nabble.com.
>



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