Dear Matthew,
Many thanks. It seem to have worked. I will post detailed analysis later. Hurry
......Thanks a ton.
( again.... phew... I was stuck on this for long time)
I will try and repay this be explaining how Aggregators work in Giraph, so that
nobody else faces this issue in future.
Following is what I understand now.1. There is an aggregator at every worker -
Let me call this as local-aggregator
2. There is another aggregator that aggregates the values for every superstep -
let me call this ss-aggregator3. There is a global aggregator which remembers
the aggregated value from previous superstep. Let me call this
master-aggregator.4. There is sometimes one extra and sometimes more than one
extra aggregator at every worker, not sure that's their role so let me call
them as extra-aggregators.
How I think it is working is:
a. The master-aggregator receives the value aggregated in previous superstep as
new value of the method aggregate(). In this method, we can access the value
sent by ss-aggregator by calling getAggregatedValue(). Thus by merging these
two values we get finally aggregated value.
b. local-aggregators send their aggregated values to ss-aggregators. It is hard
to figure out, which one out of various aggregators is the ss-aggregator.
c. Not sure what is the role of extra-aggregators.
d. It seems that the ss-aggregators get created in a superstep and get
destroyed at the end. They don't live beyond one superstep, but their value get
passed to suitable aggregator, to complete the functionality.
Is my understanding right?
Also -->
Can I print the currentSuperstep in aggregate method? ( currentSuperstep= the
superstep after which the messages are being aggregated)
Is there any way to access getConf in aggregate method, if yes how?
- Puneet
On Monday, November 17, 2014 2:36 PM, Panagiotis Eustratiadis
<[email protected]> wrote:
Hello Puneet,
I am encountering a very similar problem, and I'm studying it. I will update
this thread as soon as I find something. I think it has something to do with
the code that initializes the aggregators, but I'm not quite sure.
Regards,Eustratiadis Panagiotis.
On 17 November 2014 05:25, Puneet Agarwal <[email protected]> wrote:
I have no clue on how to resolve this issue. Any guidance in this situation can
be helpful.
Claudio - is there any detailed description of how aggregator works in Giraph
in your book?
Getting no response from anyone, should such questions be asked in developers'
list?
-PuneetIIT Delhi, India
On Sunday, November 16, 2014 12:11 PM, Puneet Agarwal
<[email protected]> wrote:
Hi All,
I have been facing a problem in Giraph for last two weeks. Following is the
detailed description, sample code, corresponding log message and a few
questions.
I will greatly appreciate any help in this regard.
Code Description:
=================
My algorithm assigns a score to select vertexes of the graph. I have to find
the best K(=5) vertexes such that their score is minimum.
I have written a Persistent Aggregator for this which takes Text value. The
snippet of the code is given below.
It works fine on my laptop (single worker), but not on the cluster of 4
computers, when running with 10 workers.
I am using Hadoop 1.0.0 and Giraph 1.0.0.
Problem Description:
====================
In the aggregator one of the previously aggregated value suddenly gets lost.
Therefore, my algorithm generates wrong results.
You can observe this in the logs, given below, in following manner
a. At line number 11, the vertex 8.4793-1 has weight 3.0, and it is the best
so far.
b. At line number 12, the aggregator receives a new value "6.1100-1,6.0",
i.e., vertex=6.1100-1 has weight=6.0
c. At line number 13, in the begining of aggregate method, the output of
getAggregatedValue() is also same as newValue.
This means it simply forgets the previously aggregated value, why so?
I have printed object-ids also, in the log messages, in order to ensure that
this is happening in the same object.
Source Code Snippet:
====================
@Override
public void aggregate(Text value) {
printLogMessage("aggregate", "MyAGG", "Entering - NewValue=", value);
printLogMessage("aggregate", "MyAGG",
"Entering - getAggregatedValue()=", getAggregatedValue());
// Main Logic is here - Omitting for simplicity
setAggregatedValue(new Text(myTopK));
printLogMessage("aggregate", "MyAGG", "Exiting AggregatedValue=",
getAggregatedValue().toString());
}
@Override
public Text createInitialValue() {
printLogMessage("=====>createInitialValue", "MyAGG",
"Entering getAggregatedValue()=", getAggregatedValue());
Text initialValue = getAggregatedValue();
if (initialValue == null) {
initialValue = new Text();
}
printLogMessage("=====>createInitialValue", "MyAGG",
"Exiting ReturnedValue=", getAggregatedValue());
return initialValue;
}
private void printLogMessage(String methodName, String prefix, String msg,
Object obj) {
if (isDebugOn(methodName)) {
if (obj == null) {
obj = "";
}
System.out.println(java.lang.System.identityHashCode(this) + "--"+
prefix + "==>" +
methodName + "() - " + msg + obj.toString());
}
}
Printed Log Messages:
=====================
1. %%%%%%%%%%%%% Entered Master Compute %%%%%%%%%%%%%%%%%%%% ====> SupsetStep
No.=2
2. 249768912--MyAGG==>=====>createInitialValue() - Entering
getAggregatedValue()=
3. 249768912--MyAGG==>=====>createInitialValue() - Exiting ReturnedValue=
4. 249768912--MyAGG==>aggregate() - Entering - NewValue=8.4793-1,3.0
5. 249768912--MyAGG==>aggregate() - Entering -
getAggregatedValue()=8.4793-1,3.0
6. 249768912--MyAGG==>aggregate() - Received AggregatedValue Again- Exiting
CurrVal=8.4793-1,3.0
7. 249768912--MyAGG==>=====>createInitialValue() - Entering
getAggregatedValue()=8.4793-1,3.0
8. 249768912--MyAGG==>=====>createInitialValue() - Exiting
ReturnedValue=8.4793-1,3.0
9. %%%%%%%%%%%%% Entered Master Compute %%%%%%%%%%%%%%%%%%%% ====> SupsetStep
No.=3
10. 249768912--MyAGG==>=====>createInitialValue() - Entering
getAggregatedValue()=8.4793-1,3.0
11. 249768912--MyAGG==>=====>createInitialValue() - Exiting
ReturnedValue=8.4793-1,3.0
12. 249768912--MyAGG==>aggregate() - Entering - NewValue=6.1100-1,6.0
13. 249768912--MyAGG==>aggregate() - Entering -
getAggregatedValue()=6.1100-1,6.0
14. 249768912--MyAGG==>aggregate() - Received AggregatedValue Again- Exiting
CurrVal=6.1100-1,6.0
15. 249768912--MyAGG==>=====>createInitialValue() - Entering
getAggregatedValue()=6.1100-1,6.0
16. 249768912--MyAGG==>=====>createInitialValue() - Exiting
ReturnedValue=6.1100-1,6.0
17. %%%%%%%%%%%%% Entered Master Compute %%%%%%%%%%%%%%%%%%%% ====> SupsetStep
No.=4
18. ...
...
My Queries:
===========
1. Why does the createInitialValue method gets called twice, in the same
superstep, on the same object of the aggregator?
2. Even if its gets called twice, why should it forget the previouly
aggregated value?
Please help me resolve this issue. This is a major problem in my work.
I am not able to proceed further because of this.
Thanks in anticipation.
- Puneet
IIT Delhi, India
