Hi Pavel,
I *think* that they are the same thing.
With C++ I've only used qpid::messaging and that *definitely* has a
default consumer capacity of 1 and I "think" a default producer capacity
of 50, so if you write a qpid::messaging consumer by default its
performance won't be great hence it's almost always a good idea to do a
setCapacity() on the consumer session to something sensible.
In Java I *think* the default is 500, but I've never had reason to mess
around with it. I only picked up on this stuff when I was ahem
"surprised" that my Java consumer was faster than my C++ consumer....
Re your question 2. according to
http://qpid.apache.org/books/0.12/Programming-In-Apache-Qpid/html/ch03s06.html
there are JVM arguments too e.g.
max_prefetch int 500 Maximum number of messages to credits.
This could also be set per connection (see connection paramters) or per
destination (see the |capacity| option under link properties in addressing).
Though that looks like receiver capacity and it sounds like you're
talking about sender capacity?
Ex. |-Dmax_prefetch=1000| property specifies the message credits to use.
There's a related Connection URL Property
|amqp://guest:guest@test/test?max_prefetch='1000'
&brokerlist='tcp://localhost:5672'|
Again it's called prefetch so I suspect this relates to the consumer
capacity in C++ qpid::messaging.
also as you've commented there's
|my-queue; {create: always, link:{capacity: 10}}
|
Again this would seem to relate to consumer capacity.
Unfortunately I can't see anything obvious in the documentation that
looks like it maps to producer capacity.
I used your comment on "setProducerCapacity" as a "seed" for a few
greps, this is called from AddressHelper in the same package
if (((Map) address.getOptions().get(LINK)).get(CAPACITY)
instanceof Map)
{
MapAccessor capacityProps = new MapAccessor(
(Map) ((Map) address.getOptions().get(LINK))
.get(CAPACITY));
link
.setConsumerCapacity(capacityProps
.getInt(CAPACITY_SOURCE) == null ? 0
: capacityProps.getInt(CAPACITY_SOURCE));
link
.setProducerCapacity(capacityProps
.getInt(CAPACITY_TARGET) == null ? 0
: capacityProps.getInt(CAPACITY_TARGET));
}
else
{
int cap = linkProps.getInt(CAPACITY) == null ? 0 :
linkProps
.getInt(CAPACITY);
link.setConsumerCapacity(cap);
link.setProducerCapacity(cap);
}
In the first block above it's talking about "CAPACITY_SOURCE" and
"CAPACITY_TARGET" in the code these are strings "source" and "target"
respectively. The first block also seems to be looking for a Map value
for the capacity property of link so I wonder......how about trying
|my-queue; {create: always, link:{capacity: {source: 50, target: 200}}}|
I haven't tried this, and I've just got there by looking at the code,
but it looks plausible. I've not come across any documentation that
covers this either, but it *might* just help.
Hmmm scratch that.. I'm typing this as I'm looking, I've just tried
"grep -rH getProducerCapacity ." and the only place where that seems to
be referenced is in Link.java, so I'm now suspecting that the above sets
the value, but nothing is using it yet....
A few more greps seem to suggest that max_prefetch relates to a session
but link capacity relates to a destination, but it looks like they do
similar things (I think they buffer messages into an internal queue on
the client runtime) but so far I've not found anything obvious about
producer capacity aside from the red herrings above, so I'm suspecting
that there's no equivalent to qpid::messaging producer setCapacity in JMS.
Sorry for rambling a bit, I hope that the train of thought is useful and
perhaps someone who knows the code a bit better can confirm what I'm seeing.
As an aside, the code base could do with a few more comments :-)
Let us know how you get on
Frase.
On 03/02/12 11:51, Pavel Moravec wrote:
Hello qpid users,
I am somehow confused about difference between capacity and maxprefetch. Both
define maximum number of messages that can be sent without receiving a response
to the first msg, but maxprefetch is applicable to consumer part of the
communication only.
My questions:
1) "maxprefetch" is applicable rather to Java client only while capacity rather
to C++, python and .NET clients.
2) How to setup capacity in Java client (to limit producers to qpid)? I tried using
address string "small-queue;{link:{capacity:'5'}}" but without an effect. I
spotted non-JMS method setProducerCapacity from org.apache.qpid.client.messaging.address
package (within class Link) but I am unable to use it via Connection, Session or
MessageProducer objects.
3) Why Programming in Apache Qpid talks about prefetch having impact to
performance, while I can't find a method to setting it in C++ client?
4) The same doc says prefetch is by default 1, while
https://cwiki.apache.org/qpid/use-priority-queues.html states it has default
value 5000 - what is correct then?
5) Are there some reasons to have those two features separated? And with
different default values (capacity has 50)?
Thanks in advance for your feedback.
Kind regards,
Pavel
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