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From Bruno Matos <bruno.ma...@paradigmaxis.pt>
Subject Re: Journal with LVQ
Date Tue, 08 Feb 2011 10:02:01 GMT

On 2011/01/19, at 14:46, Gordon Sim wrote:

> On 01/18/2011 03:31 PM, Bruno Matos wrote:
>> On 2011/01/12, at 17:33, Gordon Sim wrote:
>>> On 01/11/2011 04:30 PM, Bruno Matos wrote:
>>>> I'm publishing messages to a durable LVQ, when I run the  
>>>> publisher for
>>>> the first time the journal stays almost full, then I send the  
>>>> exact same
>>>> messages, expecting the old ones to be replaced, but after some  
>>>> time the
>>>> connection is closed with "Enqueue capacity threshold exceeded on
>>>> queue". With qpid-tool I can see that msgDepth and byteDepth are  
>>>> exactly
>>>> the same before and after the second run. Is this the expected  
>>>> behavior?
>>> Depends on what you mean by 'expected' :-)
>>> It is certainly the case that the linux journal will reach capacity
>>> with different queue depths, depending on exact sequences of  
>>> changes.
>>> i.e. the capacity is not simply a function of the final state, but
>>> also of the path to get there. In the second case there would be
>>> additional dequeue records and the file boundaries might not align  
>>> the
>>> same way etc, so the journal space can be used up for fewer enqueued
>>> messages.
>> Thank you Gordon.
>> I think I can say that's the expected to me... :) Although I need to
>> know what journal size is effectively in use, can be a percentage, is
>> that possible? I have a stored queue for browsing, like a dictionary,
>> that is updated every night, and I want to reset it only if it  
>> reaches
>> to a given percentage of journal size.
> Not sure if I understand the question correctly, but there is no  
> simple way of determining the minimum journal size needed to  
> guarantee a specific queue depth. The rule I use is to size the  
> journal much larger than I think I need (e.g. 2x the queue depth).  
> Kim has some text somewhere on the calculations involved I believe.
> Its also worth then setting a queue policy on the queue with the  
> depth fixed (and significantly less than the journal capacity). That  
> way you get a cleaner error when you hit the limit.

Sorry the delay.

I was asking if there is a way to know the used size of the journal in  
a given time. When I run my publisher for the first time, and in qpid- 
stat the queue size 2m in bytes, how can I know the effectively used  


Bruno Matos

Apache Qpid - AMQP Messaging Implementation
Project:      http://qpid.apache.org
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