3:19 a.m.
Guys,
Some interesting discussions here, keep them coming! Let me summarise what I submitted
yesterday as pull req for https://issues.jboss.org/browse/ISPN-1102
- I don't think users can really provide such accurate predictions of the objects
sizes because first java does not give you an easy way of figuring out how much your
object takes up and most of the people don't have such knowledge. What I think could
be more interesting is potentially having a buffer predictor that predicts sizes per type,
so rather than calculate the next buffer size taking all objects into account, do that per
object type. To enable to do this in the future, I'm gonna add the object to be
marshalled as parameter to https://github.com/infinispan/infinispan/pull/338/files#diff-2
- This enhancement allows for your suggestions on externalizers providing estimate size to
be implemented, but I'm not keen on that.
- For a solution to ISPN-1102, I've gone for a simpler adaptive buffer size algorithm
that Netty uses for determining the receiver buffer size. The use cases are different but
I liked the simplicity of the algorithm since calculating the next buffer size was an O(1)
op and can grow both ways very easily. I agree that it might not be as exact as reservoir
sampling+percentile, but at least it's cheaper to compute and it resolves the
immediate problem of senders keeping too much memory for sent buffers before STABLE comes
around.
- Next step would be to go and test this and compare it with Bela/Dan were seeing (+1 to
another interactive debugging session), and if we are still not too happy about the memory
consumption, maybe we can look into providing a different implementation for
BufferSizePredictor that uses R sampling.
- Finally, I think once ISPN-1102 is in, we should make the BufferSizePredictor
implementation configurable programmatically and via XML - I'll create a separate JIRA
for this.
Cheers,
On May 24, 2011, at 8:12 AM, Bela Ban wrote:
On 5/23/11 11:09 PM, Dan Berindei wrote:
>> No need to expose the ExposedByteArrayOutputStream, a byte[] buffer,
>> offset and length will do it, and we already use this today.
>>
>>
>>> In case the value is not stored in binary form, the expected life of
>>> the stream is very short anyway, after being pushed directly to
>>> network buffers we don't need it anymore... couldn't we pass the
>>> non-truncated stream directly to JGroups without this final size
>>> adjustement ?
>>
>
> The problem is that byte[] first has to be copied to another buffer
> together with the rest of the ReplicableCommand before getting to
> JGroups. AFAIK in JGroups you must have 1 buffer for each message.
If you use ExposedByteArrayOutputStream, you should have access to the
underlying buffer, so you don't need to copy it.
>> You do that, yes.
>>
>> However, afair, the issue is not on the *sending*, but on the
>> *receiving* side. That's where the larger-than-needed buffer sticks
>> around. On the sending side, as you mentioned, Infinispan passes a
>> buffer/offset/length to JGroups and JGroups passes this right on to the
>> network layer, which copies that data into a buffer.
>>
>
> I don't think so... on the receiving size the buffer size is
> controlled exclusively by JGroups, the unmarshaller doesn't create any
> buffers. The only buffers on the receiving side are those created by
> JGroups, and JGroups knows the message size before creating the buffer
> so it doesn't have to worry about predicting buffer sizes.
>
> On sending however I understood that JGroups keeps the buffer with the
> offset and length in the NakReceivingWindow exactly as it got it from
> Infinispan, without any trimming, until it receives a STABLE message
> from all the other nodes in the cluster.
Ah, ok. I think we should really do what we said before JBW, namely have
an interactive debugging session, to clear this up.
--
Bela Ban
Lead JGroups / Clustering Team
JBoss
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--
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache